Use logging.WARNING instead of logging.WARN

Use logging.WARNING instead of logging.WARN

The `WARN` constant is an undocumented alias for `WARNING`. Whilst it’s not deprecated, it’s not mentioned at all in the documentation. This references one of  `flake8-logging` plugins [rule](https://github.com/adamchainz/flake8-logging?tab=readme-ov-file#log009-warn-is-undocumented-use-warning-instead).

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### Description
Changed all uses of `logging.WARN` to `logging.WARNING`.

### Checklist
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This pull request is:

- [x] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [ ] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #1548
Pull-request: https://github.com/sqlalchemy/alembic/pull/1548
Pull-request-sha: 249b9a2942037f8da9f2db5736d1d988435b6fe5

Change-Id: I7c64ce9bb18af551c761ed9216713ee02cbbb83b