reduce test CI workflow run time

[2bndy5]

This involves saving a build per OS that can be as large as 2GB.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.53%. Comparing base (634d80d) to head (5d99c6b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   97.28%   97.53%   +0.24%     
==========================================
  Files          13       13              
  Lines        2431     2431              
==========================================
+ Hits         2365     2371       +6     
+ Misses         66       60       -6     

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[2bndy5]

I'm abandoning this effort. It didn't reduce the CI runtime as much as intended. And its too much hassle to to contend with cached file's permissions being changed through uploading/downloading them as artifacts. Using caches might help, but there's a serious concern for storage capacity allowed on GitHub's free tier.