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 89.84%. Comparing base (0fc64f8) to head (26f24ea).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #423   +/-   ##
=======================================
  Coverage   89.84%   89.84%           
=======================================
  Files          38       38           
  Lines        3103     3103           
  Branches      239      239           
=======================================
  Hits         2788     2788           
  Misses        281      281           
  Partials       34       34           

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