This PR fixes the Sphinx build failure below (see https://github.com/singhpk234/spark/runs/6799026458?check_suite_focus=true):

```
Moving to python/docs directory and building sphinx.
Running Sphinx v3.0.4
WARNING:root:'PYARROW_IGNORE_TIMEZONE' environment variable was not set. It is required to set this environment variable to '1' in both driver and executor sides if you use pyarrow>=2.0.0. pandas-on-Spark will set it for you but it does not work if there is a Spark context already launched.
/__w/spark/spark/python/pyspark/pandas/supported_api_gen.py:101: UserWarning: Warning: Latest version of pandas(>=1.4.0) is required to generate the documentation; however, your version was 1.3.5
  warnings.warn(
Warning, treated as error:
node class 'meta' is already registered, its visitors will be overridden
make: *** [Makefile:35: html] Error 2
                    ------------------------------------------------
      Jekyll 4.2.1   Please append `--trace` to the `build` command
                     for any additional information or backtrace.
                    ------------------------------------------------
```

Sphinx build fails apparently with the latest docutils (see also https://issues.apache.org/jira/browse/FLINK-24662). we should pin the version.

To recover the CI.

No, dev-only.

CI in this PR should test it out.

Closes #36813 from HyukjinKwon/SPARK-39421.

Lead-authored-by: Hyukjin Kwon <gurwls223@gmail.com>
Co-authored-by: Hyukjin Kwon <gurwls223@apache.org>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>
(cherry picked from commit c196ff4dfa1d9f1a8e20b884ee5b4a4e6e65a6e3)
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>