test_runner: print failed coverage reports with dot runner

[saitejabandaru-in]

Fixes #60884

When the coverage threshold is not met, the test runner emits a test:diagnostic event with level = "error". Previously, the dot reporter was suppressing this entirely, leading to silent failures on coverage if there were no standard test failures.
This change pushes a synthetic test failure on this condition to failedTests and increments the dot counter with an X, so it reports gracefully at the end.

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[MikeMcC399]

You have opened a PR that claims to fix issue #60884 which is already closed because it is resolved through PR #61423.

Your PR branch is also 523 commits behind the main branch.

[MikeMcC399]

#60884 was resolved through 2858f34 from #61423

This PR is therefore no longer necessary and is being closed.

It also fails linting.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.06%. Comparing base (0012a77) to head (6c6d74e).
⚠️ Report is 531 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/test_runner/reporter/dot.js	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65628      +/-   ##
==========================================
- Coverage   90.14%   90.06%   -0.08%     
==========================================
  Files         746      751       +5     
  Lines      242771   254993   +12222     
  Branches    45741    48150    +2409     
==========================================
+ Hits       218850   229669   +10819     
- Misses      15426    16499    +1073     
- Partials     8495     8825     +330     

Files with missing lines	Coverage Δ
lib/internal/test_runner/reporter/dot.js	67.14% <87.50%> (-32.86%)	⬇️

... and 296 files with indirect coverage changes

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