tests/thread: Restore gc before test case ends.

[projectgus]

Summary

Otherwise GC stays disabled (not re-enabled by soft reset) and later test runs fail with MemoryError.

Note this test case is currently disabled in CI due to "reliability issues" (as of 02b44a0). Not sure if this is the root cause of the issue in question.

Testing

• Tested on rp2 port and verified subsequent test failures went away.
• Also re-ran tests on unix port with run-tests.py -d thread, but no change expected here as a new micropython process is run for each test file.

Trade-offs and Alternatives

We could have soft reset re-enable automatic gc, instead? Would be more resilient than this fix, but might have other implications.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.42%. Comparing base (4074643) to head (739704b).

❗ Current head 739704b differs from pull request most recent head 5a778eb

Please upload reports for the commit 5a778eb to get more accurate results.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #15265   +/-   ##
=======================================
  Coverage   98.42%   98.42%           
=======================================
  Files         161      161           
  Lines       21204    21204           
=======================================
  Hits        20870    20870           
  Misses        334      334           

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[dpgeorge]

Thanks, this fix is good.

The CI reliability of these stress tests is more likely related to globals not being protected by a mutex, see related #11604.