test_runner: fix mock import eviction

[marco-ippolito]

Fixes: #59163

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.15%. Comparing base (00917ba) to head (3880570).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #64650   +/-   ##
=======================================
  Coverage   90.14%   90.15%           
=======================================
  Files         741      741           
  Lines      242076   242157   +81     
  Branches    45558    45568   +10     
=======================================
+ Hits       218216   218310   +94     
+ Misses      15385    15357   -28     
- Partials     8475     8490   +15     

Files with missing lines	Coverage Δ
lib/internal/test_runner/mock/loader.js	99.48% <100.00%> (+0.13%)	⬆️
lib/internal/test_runner/mock/mock.js	98.56% <100.00%> (+0.01%)	⬆️

... and 30 files with indirect coverage changes

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