test_runner: ensure proper teardown when tests run without isolation

[pmarchini]

This should address #57234.

Adding the teardown in case of isolation: none addresses this specific issue, and I see no potential negative effects in having it.

@cjihrig, was there a reason why we avoided it in the first place?

[nodejs-github-bot]

Review requested:

• [ ] @nodejs/test_runner

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 90.23%. Comparing base (9df0ff7) to head (dd7af59). :warning: Report is 1207 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #57394      +/-   ##
==========================================
- Coverage   90.23%   90.23%   -0.01%     
==========================================
  Files         630      630              
  Lines      185200   185214      +14     
  Branches    36233    36243      +10     
==========================================
+ Hits       167108   167120      +12     
- Misses      11056    11057       +1     
- Partials     7036     7037       +1     

Files with missing lines	Coverage Δ
lib/internal/test_runner/runner.js	89.52% <100.00%> (+0.01%)	:arrow_up:

... and 22 files with indirect coverage changes

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[pmarchini]

These changes have broken the following test:

https://github.com/nodejs/node/blob/96457b433fb1b9cdcc7d957914ae815aa40a5c78/test/parallel/test-runner-extraneous-async-activity.js#L52-L68

I'm taking a look!