Don't report coverage on test directory

[maxrjones]

This configures code coverage to ignore the test directory, which I think isn't useful.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.33%. Comparing base (69bc233) to head (01f4b3a).
⚠️ Report is 1 commits behind head on main.

❌ Your project status has failed because the head coverage (99.33%) is below the target coverage (100.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #803      +/-   ##
==========================================
+ Coverage   98.68%   99.33%   +0.64%     
==========================================
  Files          64       26      -38     
  Lines        2595      898    -1697     
==========================================
- Hits         2561      892    -1669     
+ Misses         34        6      -28     

see 39 files with indirect coverage changes

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