chore: drop support for Python 3.8

[nijel]

Proposed changes

Fixes #946

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.91%. Comparing base (326d4b3) to head (25bf8ec).
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #955      +/-   ##
==========================================
+ Coverage   77.88%   77.91%   +0.02%     
==========================================
  Files         347      347              
  Lines       10669    10678       +9     
  Branches      504      452      -52     
==========================================
+ Hits         8310     8320      +10     
- Misses       2200     2201       +1     
+ Partials      159      157       -2     

Flag	Coverage Δ
unittests	77.91% <ø> (+0.02%)	⬆️

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