Deprecation: Add stacklevel=2 to make calling code clear

[hugovk]

Summary of changes

Before

Points to deprecation itself in setuptools, /Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/site-packages/setuptools/config/__init__.py:

================================================================== warnings summary ==================================================================
pyroma/tests.py::RatingsTest::test_only_config
  /Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/site-packages/setuptools/config/__init__.py:28: SetuptoolsDeprecationWarning: As setuptools moves its configuration towards `pyproject.toml`,
  `setuptools.config.read_configuration` became deprecated.

  For the time being, you can use the `setuptools.config.setupcfg` module
  to access a backward compatible API, but this module is provisional
  and might be removed in the future.

    warnings.warn(dedent(msg), SetuptoolsDeprecationWarning)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================================================== 12 passed, 1 warning in 3.83s ============================================================

After

Points to caller of deprecation in user's project, for example /private/tmp/pyroma/pyroma/projectdata.py:

================================================================== warnings summary ==================================================================
pyroma/tests.py::RatingsTest::test_only_config
  /private/tmp/pyroma/pyroma/projectdata.py:50: SetuptoolsDeprecationWarning: As setuptools moves its configuration towards `pyproject.toml`,
  `setuptools.config.read_configuration` became deprecated.

  For the time being, you can use the `setuptools.config.setupcfg` module
  to access a backward compatible API, but this module is provisional
  and might be removed in the future.

    data = config.read_configuration("setup.cfg")

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================================================== 12 passed, 1 warning in 3.73s ============================================================

Docs: https://docs.python.org/3/library/warnings.html#available-functions

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d/.
  (See documentation for details)

[abravalheri]

Thank you very much @hugovk.