[Python] Handle pytest 8 deprecations about pytest.warns(None)

[asfimport]

We have a few warnings about that when running the tests, for example:

pyarrow/tests/test_pandas.py::TestConvertMetadata::test_rangeindex_doesnt_warn
pyarrow/tests/test_pandas.py::TestConvertMetadata::test_multiindex_doesnt_warn
  /home/joris/miniconda3/envs/arrow-dev/lib/python3.10/site-packages/_pytest/python.py:192: PytestRemovedIn8Warning: Passing None has been deprecated.
  See https://docs.pytest.org/en/latest/how-to/capture-warnings.html#additional-use-cases-of-warnings-in-tests for alternatives in common use cases.
    result = testfunction(**testargs)

Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: Miles Granger / @milesgranger

Related issues:

• [Python] Reduce warnings during tests (is a child of)

_{Note: This issue was originally created as ARROW-18125. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
Issue resolved by pull request 14729
#14729