[ci] Remove gnu-tar workaround.

[anp]

It's now installed on macOS images by default and the cache action has been updated to use it. I think it's safe to remove all of our workaround configuration for the issue.

[codecov]

Codecov Report

Merging #250 (5dbdecf) into main (20920ca) will decrease coverage by 0.35%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #250      +/-   ##
==========================================
- Coverage   49.72%   49.36%   -0.36%     
==========================================
  Files          46       46              
  Lines        8443     8443              
==========================================
- Hits         4198     4168      -30     
- Misses       4245     4275      +30     

Impacted Files	Coverage Δ
src/runtime.rs	40.57% <0.00%> (-5.27%)	⬇️
src/runtime/context.rs	97.64% <0.00%> (+1.17%)	⬆️

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