TypeError when loading from GCP bucket
### Describe the bug

Loading a dataset from a GCP bucket raises a type error. This bug was introduced recently (either in 2.14 or 2.14.1), and appeared during a migration from 2.13.1.

### Steps to reproduce the bug

Load any file from a GCP bucket:

```python
import datasets

datasets.load_dataset("json", data_files=["gs://..."])
```

The following exception is raised:

```python
Traceback (most recent call last):
...
packages/datasets/data_files.py", line 335, in resolve_pattern
    protocol_prefix = fs.protocol + "://" if fs.protocol != "file" else ""
TypeError: can only concatenate tuple (not "str") to tuple
```

With a `GoogleFileSystem`, the attribute `fs.protocol` is a tuple `('gs', 'gcs')` and hence cannot be concatenated with a string.


### Expected behavior

The file should be loaded without exception.

### Environment info

- `datasets` version: 2.14.1
- Platform: macOS-13.2.1-x86_64-i386-64bit
- Python version: 3.10.12
- Huggingface_hub version: 0.16.4
- PyArrow version: 12.0.1
- Pandas version: 2.0.3
