🧪 Bump MyPy Python to 3.9 @ pre-commit config

[Mr-Sunglasses]

The pre-commit.ci service dropped support for Python 3.8 as it's
gone EOL. This change makes the check runnable again. It is suboptimal
as we haven't yet dropped support for Python 3.8. #2144 will address
the underlying issue more thoroughly.

Resolves #2133.

Contributor checklist

• Included tests for the changes.
• PR title is short, clear, and ready to be included in the user-facing changelog.

Maintainer checklist

• Verified one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[webknjaz]

Please include the explanation of what is broken so it'd obvious if anything is actually being fixed or changed arbitrarily. Add an explanation of why it fixes the thing and why it was broken.

Also, we have to consider that this makes the runtimes inconsistent across the checks, and they should normally have the lowest supported runtime. If Python 3.8 support is being dropped, this should include dropping support from all the places, not just one.

[macro1]

@webknjaz this is broken because the pre-commit GitHub Action no longer supports Python 3.8. it's not an issue with the project, it's a simple CI configuration adjustment

[webknjaz]

Wait, can you point out where GHA runs pre-commit? I thought we only got pre-commit.ci doing this...

[webknjaz]

I've converted this to draft to prevent accidental merging ahead of time.

[webknjaz]

This will be a part of the combined CI fix. Please do not add any changes to this PR.