Replace deprecated logging.warn with logging.warning

[hugovk]

Replace logging.warn (deprecated in Python 2.7, 2011) with logging.warning (added in Python 2.3, 2003).

• https://docs.python.org/3/library/logging.html#logging.Logger.warning
• logging.warn() is not documented python/cpython#57444

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• Stay on point and keep it small so it can be easily reviewed. For example, try to apply any general refactoring separately outside of the PR.
• Consider adding unit tests, especially for bug fixes. If you don't, tell us why.

Replacing deprecated function with one which has been around since 2.3.

• All new and existing tests pass, with 100% test coverage (make test-coverage)
• Linting passes (make lint)
• Consider updating documentation. If you don't, tell us why.

Not big enough for docs.

• List the environments / platforms in which you tested your changes.

macOS / Python 3.10

Thanks for contributing to this project!

[thibaudcolas]

Well, TIL! Thank you for picking this up. I’m really surprised this hasn’t been flagged by python -X dev -W error example.py even though it clearly seems to be deprecated.