CI: inherit secrets in coverage workflow

[ohmyfelix]

What changed

• Added secrets: inherit to .github/workflows/coverage.yml so the reusable coverage workflow receives repository secrets from the caller.

Why

• The coverage workflow rollout for Roll out secrets: inherit for reusable coverage workflows contributte#74 requires reusable workflow callers to explicitly inherit secrets so coverage-related tokens remain available in CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.50%. Comparing base (b90e7fd) to head (55173c6).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
- Coverage   78.04%   77.50%   -0.55%     
==========================================
  Files           2        2              
  Lines         123      120       -3     
==========================================
- Hits           96       93       -3     
  Misses         27       27              

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