chore: pin GitHub Actions workflows to full commit SHAs

[irfanuddinahmad]

Pins all uses: action refs to their full commit SHA with the version tag preserved as a comment. Part of org-wide SHA-pinning migration: openedx/.github#165

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.00%. Comparing base (3c1b630) to head (29bfab0).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #682   +/-   ##
=======================================
  Coverage   86.00%   86.00%           
=======================================
  Files          27       27           
  Lines         443      443           
  Branches      104      102    -2     
=======================================
  Hits          381      381           
  Misses         61       61           
  Partials        1        1           

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