ci: test python 3.8

[codecov[bot]]

Codecov Report

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

Comparison is base (0d0dfd3) 24.48% compared to head (8447010) 24.53%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #136 +/- ## ========================================== + Coverage 24.48% 24.53% +0.05% ========================================== Files 211 211 Lines 17649 17609 -40 ========================================== Hits 4321 4321 + Misses 13328 13288 -40 ```

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