Drop python 3.9

[codecov[bot]]

Codecov Report

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

Project coverage is 96.03%. Comparing base (9805f9f) to head (afaa2c5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #230 +/- ## ========================================== - Coverage 96.05% 96.03% -0.02% ========================================== Files 89 89 Lines 8011 7972 -39 ========================================== - Hits 7695 7656 -39 Misses 316 316 ```

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