ci: keep coverage stable with pytest-cov 7

[MilesCranmerBot]

Supersedes dependabot PR #1031.

• Allow pytest-cov<8 (so we can pick up pytest-cov 7)
• Pin coverage to >=7.10.6 to match pytest-cov 7 requirements

Note: CI uses coverage run directly (not pytest-cov) and already has subprocess coverage startup configured via COVERAGE_PROCESS_START + coverage.process_startup().

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.25%. Comparing base (2ac7e71) to head (527ef22).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1139      +/-   ##
==========================================
+ Coverage   93.91%   94.25%   +0.33%     
==========================================
  Files          21       21              
  Lines        1643     1687      +44     
==========================================
+ Hits         1543     1590      +47     
+ Misses        100       97       -3     

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