remove python 3.8 dependency from buildtest

[codecov[bot]]

Codecov Report

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

Project coverage is 80.20%. Comparing base (50722cf) to head (c7a26f2). Report is 34 commits behind head on devel.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #1829 +/- ## ========================================== - Coverage 80.96% 80.20% -0.77% ========================================== Files 59 59 Lines 6608 6595 -13 Branches 1274 1143 -131 ========================================== - Hits 5350 5289 -61 - Misses 1257 1305 +48 Partials 1 1 ```

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