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 98.49%. Comparing base (2df48e4) to head (89c5d17).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #516   +/-   ##
=======================================
  Coverage   98.49%   98.49%           
=======================================
  Files          21       21           
  Lines        1261     1261           
  Branches       75       75           
=======================================
  Hits         1242     1242           
  Misses         19       19           

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