CompatHelper: bump compat for Makie to 0.21, (keep existing compat)

[github-actions[bot]]

This pull request changes the compat entry for the Makie package from 0.20 to 0.20, 0.21. This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov[bot]]

Codecov Report

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

Project coverage is 90.34%. Comparing base (5bcf055) to head (1a59279). Report is 19 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #185 +/- ## ========================================== - Coverage 91.59% 90.34% -1.25% ========================================== Files 11 11 Lines 761 808 +47 ========================================== + Hits 697 730 +33 - Misses 64 78 +14 ```

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