Fix flaky InstrumentGarbageCollectionBenchmarkTest

[asafm]

Fixes #6211

• Adds more leniency towards tests, has fewer options to "mess" them and lower the allocation rate, and is more prone to have a variable allocation rate.
• Constraints the InstrumentGarbageCollectionBenchmarkTest to run only in one specific environment out of the entire matrix

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (695ed53) 91.02% compared to head (0f46f80) 91.04%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6221      +/-   ##
============================================
+ Coverage     91.02%   91.04%   +0.01%     
- Complexity     5686     5687       +1     
============================================
  Files           621      621              
  Lines         16642    16642              
  Branches       1703     1703              
============================================
+ Hits          15149    15152       +3     
+ Misses         1000      998       -2     
+ Partials        493      492       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[asafm]

@jack-berg I had to add another file. Tell me if that's ok.