We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
DOC: update read_postgis docstring for CRS changes
The read_postgis docstring still mentions to use a dict:

https://github.com/geopandas/geopandas/blob/078062d303e401aaa5e37e04c0e7c3ce188920fe/geopandas/io/sql.py#L33-L36

we should update this to follow how CRS is explained in other places now we use pyproj.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `geopandas/io/sql.py`
Content:
```
1 import sys
2 
3 import pandas as pd
4 
5 import shapely.wkb
6 
7 from geopandas import GeoDataFrame
8 
9 
10 def read_postgis(
11     sql,
12     con,
13     geom_col="geom",
14     crs=None,
15     index_col=None,
16     coerce_float=True,
17     parse_dates=None,
18     params=None,
19 ):
20     """
21     Returns a GeoDataFrame corresponding to the result of the query
22     string, which must contain a geometry column in WKB representation.
23 
24     Parameters
25     ----------
26     sql : string
27         SQL query to execute in selecting entries from database, or name
28         of the table to read from the database.
29     con : DB connection object or SQLAlchemy engine
30         Active connection to the database to query.
31     geom_col : string, default 'geom'
32         column name to convert to shapely geometries
33     crs : dict or str, optional
34         CRS to use for the returned GeoDataFrame; if not set, tries to
35         determine CRS from the SRID associated with the first geometry in
36         the database, and assigns that to all geometries.
37 
38     See the documentation for pandas.read_sql for further explanation
39     of the following parameters:
40     index_col, coerce_float, parse_dates, params
41 
42     Returns
43     -------
44     GeoDataFrame
45 
46     Example
47     -------
48     PostGIS
49     >>> sql = "SELECT geom, kind FROM polygons"
50     SpatiaLite
51     >>> sql = "SELECT ST_AsBinary(geom) AS geom, kind FROM polygons"
52     >>> df = geopandas.read_postgis(sql, con)
53     """
54 
55     df = pd.read_sql(
56         sql,
57         con,
58         index_col=index_col,
59         coerce_float=coerce_float,
60         parse_dates=parse_dates,
61         params=params,
62     )
63 
64     if geom_col not in df:
65         raise ValueError("Query missing geometry column '{}'".format(geom_col))
66 
67     geoms = df[geom_col].dropna()
68 
69     if not geoms.empty:
70         load_geom_bytes = shapely.wkb.loads
71         """Load from Python 3 binary."""
72 
73         def load_geom_buffer(x):
74             """Load from Python 2 binary."""
75             return shapely.wkb.loads(str(x))
76 
77         def load_geom_text(x):
78             """Load from binary encoded as text."""
79             return shapely.wkb.loads(str(x), hex=True)
80 
81         if sys.version_info.major < 3:
82             if isinstance(geoms.iat[0], buffer):
83                 load_geom = load_geom_buffer
84             else:
85                 load_geom = load_geom_text
86         elif isinstance(geoms.iat[0], bytes):
87             load_geom = load_geom_bytes
88         else:
89             load_geom = load_geom_text
90 
91         df[geom_col] = geoms = geoms.apply(load_geom)
92         if crs is None:
93             srid = shapely.geos.lgeos.GEOSGetSRID(geoms.iat[0]._geom)
94             # if no defined SRID in geodatabase, returns SRID of 0
95             if srid != 0:
96                 crs = "epsg:{}".format(srid)
97 
98     return GeoDataFrame(df, crs=crs, geometry=geom_col)
99
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/geopandas/io/sql.py b/geopandas/io/sql.py
--- a/geopandas/io/sql.py
+++ b/geopandas/io/sql.py
@@ -30,10 +30,12 @@
         Active connection to the database to query.
     geom_col : string, default 'geom'
         column name to convert to shapely geometries
-    crs : dict or str, optional
-        CRS to use for the returned GeoDataFrame; if not set, tries to
-        determine CRS from the SRID associated with the first geometry in
-        the database, and assigns that to all geometries.
+    crs : pyproj.CRS, optional
+        CRS to use for the returned GeoDataFrame. The value can be anything accepted
+        by :meth:`pyproj.CRS.from_user_input() <pyproj.crs.CRS.from_user_input>`,
+        such as an authority string (eg "EPSG:4326") or a WKT string.
+        If not set, tries to determine CRS from the SRID associated with the
+        first geometry in the database, and assigns that to all geometries.
 
     See the documentation for pandas.read_sql for further explanation
     of the following parameters:

{"golden_diff": "diff --git a/geopandas/io/sql.py b/geopandas/io/sql.py\n--- a/geopandas/io/sql.py\n+++ b/geopandas/io/sql.py\n@@ -30,10 +30,12 @@\n         Active connection to the database to query.\n     geom_col : string, default 'geom'\n         column name to convert to shapely geometries\n-    crs : dict or str, optional\n-        CRS to use for the returned GeoDataFrame; if not set, tries to\n-        determine CRS from the SRID associated with the first geometry in\n-        the database, and assigns that to all geometries.\n+    crs : pyproj.CRS, optional\n+        CRS to use for the returned GeoDataFrame. The value can be anything accepted\n+        by :meth:`pyproj.CRS.from_user_input() <pyproj.crs.CRS.from_user_input>`,\n+        such as an authority string (eg \"EPSG:4326\") or a WKT string.\n+        If not set, tries to determine CRS from the SRID associated with the\n+        first geometry in the database, and assigns that to all geometries.\n \n     See the documentation for pandas.read_sql for further explanation\n     of the following parameters:\n", "issue": "DOC: update read_postgis docstring for CRS changes\nThe read_postgis docstring still mentions to use a dict:\r\n\r\nhttps://github.com/geopandas/geopandas/blob/078062d303e401aaa5e37e04c0e7c3ce188920fe/geopandas/io/sql.py#L33-L36\r\n\r\nwe should update this to follow how CRS is explained in other places now we use pyproj.\n", "before_files": [{"content": "import sys\n\nimport pandas as pd\n\nimport shapely.wkb\n\nfrom geopandas import GeoDataFrame\n\n\ndef read_postgis(\n    sql,\n    con,\n    geom_col=\"geom\",\n    crs=None,\n    index_col=None,\n    coerce_float=True,\n    parse_dates=None,\n    params=None,\n):\n    \"\"\"\n    Returns a GeoDataFrame corresponding to the result of the query\n    string, which must contain a geometry column in WKB representation.\n\n    Parameters\n    ----------\n    sql : string\n        SQL query to execute in selecting entries from database, or name\n        of the table to read from the database.\n    con : DB connection object or SQLAlchemy engine\n        Active connection to the database to query.\n    geom_col : string, default 'geom'\n        column name to convert to shapely geometries\n    crs : dict or str, optional\n        CRS to use for the returned GeoDataFrame; if not set, tries to\n        determine CRS from the SRID associated with the first geometry in\n        the database, and assigns that to all geometries.\n\n    See the documentation for pandas.read_sql for further explanation\n    of the following parameters:\n    index_col, coerce_float, parse_dates, params\n\n    Returns\n    -------\n    GeoDataFrame\n\n    Example\n    -------\n    PostGIS\n    >>> sql = \"SELECT geom, kind FROM polygons\"\n    SpatiaLite\n    >>> sql = \"SELECT ST_AsBinary(geom) AS geom, kind FROM polygons\"\n    >>> df = geopandas.read_postgis(sql, con)\n    \"\"\"\n\n    df = pd.read_sql(\n        sql,\n        con,\n        index_col=index_col,\n        coerce_float=coerce_float,\n        parse_dates=parse_dates,\n        params=params,\n    )\n\n    if geom_col not in df:\n        raise ValueError(\"Query missing geometry column '{}'\".format(geom_col))\n\n    geoms = df[geom_col].dropna()\n\n    if not geoms.empty:\n        load_geom_bytes = shapely.wkb.loads\n        \"\"\"Load from Python 3 binary.\"\"\"\n\n        def load_geom_buffer(x):\n            \"\"\"Load from Python 2 binary.\"\"\"\n            return shapely.wkb.loads(str(x))\n\n        def load_geom_text(x):\n            \"\"\"Load from binary encoded as text.\"\"\"\n            return shapely.wkb.loads(str(x), hex=True)\n\n        if sys.version_info.major < 3:\n            if isinstance(geoms.iat[0], buffer):\n                load_geom = load_geom_buffer\n            else:\n                load_geom = load_geom_text\n        elif isinstance(geoms.iat[0], bytes):\n            load_geom = load_geom_bytes\n        else:\n            load_geom = load_geom_text\n\n        df[geom_col] = geoms = geoms.apply(load_geom)\n        if crs is None:\n            srid = shapely.geos.lgeos.GEOSGetSRID(geoms.iat[0]._geom)\n            # if no defined SRID in geodatabase, returns SRID of 0\n            if srid != 0:\n                crs = \"epsg:{}\".format(srid)\n\n    return GeoDataFrame(df, crs=crs, geometry=geom_col)\n", "path": "geopandas/io/sql.py"}], "after_files": [{"content": "import sys\n\nimport pandas as pd\n\nimport shapely.wkb\n\nfrom geopandas import GeoDataFrame\n\n\ndef read_postgis(\n    sql,\n    con,\n    geom_col=\"geom\",\n    crs=None,\n    index_col=None,\n    coerce_float=True,\n    parse_dates=None,\n    params=None,\n):\n    \"\"\"\n    Returns a GeoDataFrame corresponding to the result of the query\n    string, which must contain a geometry column in WKB representation.\n\n    Parameters\n    ----------\n    sql : string\n        SQL query to execute in selecting entries from database, or name\n        of the table to read from the database.\n    con : DB connection object or SQLAlchemy engine\n        Active connection to the database to query.\n    geom_col : string, default 'geom'\n        column name to convert to shapely geometries\n    crs : pyproj.CRS, optional\n        CRS to use for the returned GeoDataFrame. The value can be anything accepted\n        by :meth:`pyproj.CRS.from_user_input() <pyproj.crs.CRS.from_user_input>`,\n        such as an authority string (eg \"EPSG:4326\") or a WKT string.\n        If not set, tries to determine CRS from the SRID associated with the\n        first geometry in the database, and assigns that to all geometries.\n\n    See the documentation for pandas.read_sql for further explanation\n    of the following parameters:\n    index_col, coerce_float, parse_dates, params\n\n    Returns\n    -------\n    GeoDataFrame\n\n    Example\n    -------\n    PostGIS\n    >>> sql = \"SELECT geom, kind FROM polygons\"\n    SpatiaLite\n    >>> sql = \"SELECT ST_AsBinary(geom) AS geom, kind FROM polygons\"\n    >>> df = geopandas.read_postgis(sql, con)\n    \"\"\"\n\n    df = pd.read_sql(\n        sql,\n        con,\n        index_col=index_col,\n        coerce_float=coerce_float,\n        parse_dates=parse_dates,\n        params=params,\n    )\n\n    if geom_col not in df:\n        raise ValueError(\"Query missing geometry column '{}'\".format(geom_col))\n\n    geoms = df[geom_col].dropna()\n\n    if not geoms.empty:\n        load_geom_bytes = shapely.wkb.loads\n        \"\"\"Load from Python 3 binary.\"\"\"\n\n        def load_geom_buffer(x):\n            \"\"\"Load from Python 2 binary.\"\"\"\n            return shapely.wkb.loads(str(x))\n\n        def load_geom_text(x):\n            \"\"\"Load from binary encoded as text.\"\"\"\n            return shapely.wkb.loads(str(x), hex=True)\n\n        if sys.version_info.major < 3:\n            if isinstance(geoms.iat[0], buffer):\n                load_geom = load_geom_buffer\n            else:\n                load_geom = load_geom_text\n        elif isinstance(geoms.iat[0], bytes):\n            load_geom = load_geom_bytes\n        else:\n            load_geom = load_geom_text\n\n        df[geom_col] = geoms = geoms.apply(load_geom)\n        if crs is None:\n            srid = shapely.geos.lgeos.GEOSGetSRID(geoms.iat[0]._geom)\n            # if no defined SRID in geodatabase, returns SRID of 0\n            if srid != 0:\n                crs = \"epsg:{}\".format(srid)\n\n    return GeoDataFrame(df, crs=crs, geometry=geom_col)\n", "path": "geopandas/io/sql.py"}]}