Python upgrade: Stop testing 3.8, start testing 3.13

[jku]

We don't strictly require 3.9 yet but likely should soon as the container annotation features are nice.

I'll file an issue on those annotations

[coveralls]

Pull Request Test Coverage Report for Build 11361566830

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 96.606%

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Totals
Change from base Build 11341086819:	-0.2%
Covered Lines:	1569
Relevant Lines:	1606

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💛 - Coveralls

[jku]

Once there's a review here, I will change the expected test names (currently the expectation is Tests (3.12, ...) but I changed the name to Tests (3.x, ...) since we don't really care about the specific version in these two test runs)