fix: exclude branches on ignored lines from coverage reports

[JeevanYewale]

Issue

When using /* node:coverage ignore next */ comments, the DA (line coverage) entries are correctly excluded from the LCOV output, but BRDA (branch coverage) entries for branches leading to ignored lines remain as uncovered. This causes false branch coverage failures.

Problem

• DA entries are excluded
• BRDA entries are NOT excluded
• Results in incorrect branch coverage percentages (e.g., 66.67% instead of 100%)
• Breaks CI/CD pipelines with branch coverage thresholds

Solution

Modified lib/internal/test_runner/coverage.js to exclude branches that are entirely on ignored lines from the branch coverage totals, matching the behavior of line coverage exclusion.

Changes

• Only include branches in branchReports if they are not entirely on ignored lines
• Ensures consistency with c8 and other coverage tools
• Fixes test_runner: node:coverage ignore comments exclude DA but leave BRDA in lcov output #61586

Testing

The fix can be verified with the minimal reproduction case from the issue:
https://github.com/tobigumo/node-coverage-brda-bug

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[MoLow]

Please add/adjust tests (might want for ci completion to see if there are any failures, or just run python3 tools/test.py "test/test-runner/*" and python3 tools/test.py "test/parallel/test-runner-*)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.72%. Comparing base (3fc542e) to head (48310bc).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61648      +/-   ##
==========================================
- Coverage   89.72%   89.72%   -0.01%     
==========================================
  Files         674      674              
  Lines      204360   204363       +3     
  Branches    39269    39265       -4     
==========================================
+ Hits       183370   183372       +2     
- Misses      13301    13302       +1     
  Partials     7689     7689              

Files with missing lines	Coverage Δ
lib/internal/test_runner/coverage.js	73.03% <100.00%> (+0.11%)	⬆️

... and 23 files with indirect coverage changes

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