test(gcp-detector): properly isolate GcpDetectorIntegration.test.ts

[aabmass]

Which problem is this PR solving?

Isolate GcpDetectorIntegration.test.ts (using runTestFixture()) so that it doesn't leak it's changes into other test cases

Short description of the changes

This was breaking some tests I am working on for #2933 (comment). It also just overall simplifies the test since we don't need to play with require.cache.

I verified this test fails properly without suppressTracing() in the detector.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.55%. Comparing base (35c7754) to head (ec59f53).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3005   +/-   ##
=======================================
  Coverage   89.55%   89.55%           
=======================================
  Files         193      193           
  Lines        9698     9698           
  Branches     2011     2011           
=======================================
  Hits         8685     8685           
  Misses       1013     1013           

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[pichlermarc]

looks good 👍