Improve GitHub Actions workflow security

[jwodder]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.85%. Comparing base (7723839) to head (2d08d27).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #39   +/-   ##
=======================================
  Coverage   96.85%   96.85%           
=======================================
  Files           3        3           
  Lines         413      413           
  Branches       52       52           
=======================================
  Hits          400      400           
  Misses         10       10           
  Partials        3        3           

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