⬆️ Drop support for Python 3.9

[chrisjsewell]

This is EoL next month https://devguide.python.org/versions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.77%. Comparing base (9ffe841) to head (1973d78).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
+ Coverage   95.44%   95.77%   +0.32%     
==========================================
  Files          64       64              
  Lines        3402     3429      +27     
==========================================
+ Hits         3247     3284      +37     
+ Misses        155      145      -10     

Flag	Coverage Δ
pytests	95.77% <100.00%> (+0.32%)	⬆️

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