test_runner: report load errors with --test-isolation=none

[lazerg]

With --test-isolation=none, a test file that throws while loading after it has already registered a test was reported as passing. The import error was caught but only reported through the placeholder test, which was added only when the file registered no tests, so the error was dropped and the run exited 0.

This adds the placeholder test whenever the import throws, so the error is shown and the run fails like it does with process isolation.

Fixes: #66549

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[github-actions]

Caution

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.40%. Comparing base (9a85290) to head (b15873e).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66550      +/-   ##
==========================================
- Coverage   90.40%   90.40%   -0.01%     
==========================================
  Files         791      791              
  Lines      276120   276120              
  Branches    53032    53019      -13     
==========================================
- Hits       249634   249630       -4     
+ Misses      16896    16895       -1     
- Partials     9590     9595       +5     

Files with missing lines	Coverage Δ
lib/internal/test_runner/runner.js	95.13% <100.00%> (ø)

... and 25 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78199/