gha: remove env vars SHELL

[skshetry]

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• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Thank you for the contribution - we'll try to review it as soon as possible. 🙏

[codecov]

Codecov Report

Base: 93.54% // Head: 93.54% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (b549034) compared to base (b25ef5c).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8737   +/-   ##
=======================================
  Coverage   93.54%   93.54%           
=======================================
  Files         457      457           
  Lines       36254    36255    +1     
  Branches     5262     5262           
=======================================
+ Hits        33914    33915    +1     
  Misses       1835     1835           
  Partials      505      505           

Impacted Files	Coverage Δ
tests/func/test_repro.py	99.05% <100.00%> (+<0.01%)	⬆️

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[efiop]

@skshetry What's the status here?

[skshetry]

will pick it up after I am done with index cleanup. There's one test failing that has to be fixed.