CompatHelper: bump compat for Makie to 0.20, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Makie package from 0.19 to 0.19, 0.20.
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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d7ad5b1) 72.87% compared to head (a734007) 82.04%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   72.87%   82.04%   +9.16%     
==========================================
  Files          29       28       -1     
  Lines        1132      997     -135     
==========================================
- Hits          825      818       -7     
+ Misses        307      179     -128     

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