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 87.86%. Comparing base (004cc23) to head (7539239).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #883   +/-   ##
=======================================
  Coverage   87.86%   87.86%           
=======================================
  Files          50       50           
  Lines        1483     1483           
  Branches      301      298    -3     
=======================================
  Hits         1303     1303           
+ Misses        169      167    -2     
- Partials       11       13    +2     

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