Remove astropy test runner

[pllim]

Fix #171

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.10%. Comparing base (7b78df5) to head (2fecf9c).
Report is 54 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #172      +/-   ##
==========================================
- Coverage   93.92%   90.10%   -3.83%     
==========================================
  Files          37       41       +4     
  Lines        1598     2184     +586     
==========================================
+ Hits         1501     1968     +467     
- Misses         97      216     +119     

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[pllim]

devdeps failure unrelated

[kecnry]

Thanks!