Drop support for Python 3.8

[hugovk]

Python 3.8 EOL is due tomorrow, when 3.13.0 final is released.

• https://devguide.python.org/versions/
• https://peps.python.org/pep-0569/

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.86%. Comparing base (9c82f70) to head (4d31928). Report is 7 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #598 +/- ## ========================================== + Coverage 92.66% 92.86% +0.20% ========================================== Files 28 28 Lines 2958 3057 +99 ========================================== + Hits 2741 2839 +98 - Misses 217 218 +1 ```

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[hugovk]

I think we're due for a release, I can do it later today.