TST: astropy 5.0rc2

[pllim]

Description

This pull request is to test against astropy 5.0rc2

[github-actions]

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[codecov]

Codecov Report

Merging #156 (1731924) into master (3ca4a4d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #156   +/-   ##
=======================================
  Coverage   84.87%   84.87%           
=======================================
  Files          13       13           
  Lines        1633     1633           
=======================================
  Hits         1386     1386           
  Misses        247      247           

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[pllim]

Will keep this open until I can re-test with new stable synphot.

[pllim]

RTD failure can be ignored. astropy 5.0rc2 looks good!