Drop Python 3.9 support

[cthoyt]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.10%. Comparing base (78382c7) to head (05288f0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
- Coverage   93.48%   93.10%   -0.39%     
==========================================
  Files          12       12              
  Lines         522      522              
  Branches       82       82              
==========================================
- Hits          488      486       -2     
- Misses         24       25       +1     
- Partials       10       11       +1     

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