[WIP] Fix failing GitHub Actions job for coverage

[Copilot]

• Identify root cause: codecov/codecov-action@v4 SHA not downloadable in CI
• Update codecov/codecov-action from v4 to v5 in .github/workflows/coverage.yml

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.02%. Comparing base (98bb94d) to head (d7d5876).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #134   +/-   ##
=======================================
  Coverage   85.02%   85.02%           
=======================================
  Files          13       13           
  Lines        2879     2879           
=======================================
  Hits         2448     2448           
  Misses        431      431           

Flag	Coverage Δ
unittests	85.02% <ø> (ø)

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