STYLE: Fix redefined-outer-name linting issue
Part of the fix for #49656
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Looks pretty good, you'll probably also need to change

https://github.com/pandas-dev/pandas/blob/fd8e3e773887c0ba9721406b3034494fff2c2567/pandas/tests/plotting/test_converter.py#L218

to `converter.mdates` (and elsewhere in that file) Done, thanks for the quick review! 🤔 not sure why one CI job has failed - I've restarted it as it looks unrelated Thanks, all green now! 😄 