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 95.33%. Comparing base (c0af4be) to head (e05be56).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #225   +/-   ##
=======================================
  Coverage   95.33%   95.33%           
=======================================
  Files          69       69           
  Lines        8075     8075           
  Branches      429      429           
=======================================
  Hits         7698     7698           
  Misses        283      283           
  Partials       94       94           

Flag	Coverage Δ
unittests	95.33% <ø> (ø)

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