GitHub Actions: Test on Python 3.8, 3.9, 3.10, 3.11, 3.12

[cclauss]

Proposed changes

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request.

Fixes

If it fixes a bug or resolves a feature request, be sure to link to that issue.

Types of changes

What types of changes does your code introduce to pythomata?
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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• I have read the CONTRIBUTING doc
• I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...