Mark CI tests as xfail when 502 error
To make CI more robust, we could mark as xfail when the Hub raises a 502 error (besides 500 error):

- FAILED tests/test_upstream_hub.py::TestPushToHub::test_push_dataset_to_hub_skip_identical_files
  - https://github.com/huggingface/datasets/actions/runs/3174626525/jobs/5171672431
  ```
  >           raise HTTPError(http_error_msg, response=self)
  E           requests.exceptions.HTTPError: 502 Server Error: Bad Gateway for url: https://hub-ci.huggingface.co/datasets/__DUMMY_TRANSFORMERS_USER__/test-16648055339047.git/info/lfs/objects/batch
  ```

- FAILED tests/test_upstream_hub.py::TestPushToHub::test_push_dataset_dict_to_hub_overwrite_files
  - https://github.com/huggingface/datasets/actions/runs/3145587033/jobs/5113074889
  ```
  >           raise HTTPError(http_error_msg, response=self)
  E           requests.exceptions.HTTPError: 502 Server Error: Bad Gateway for url: https://hub-ci.huggingface.co/datasets/__DUMMY_TRANSFORMERS_USER__/test-16643866807322.git/info/lfs/objects/verify
  ```

Currently, we mark as xfail when 500 error:
- #4845