Make a test scenario less stressful.

[VSadov]

Test-only fix.

Fixes: #119187

The testcase creates and joins threads in a loop while another thread calls GetTotalAllocatedBytes and checks various invariants: if the result is not negative, grows over time, ...
This is not a stress test. The purpose is just to demonstrate that GetTotalAllocatedBytes works in the presence of threads starting and exiting. It does not need to run for very long.

Creating/joining threads nonstop appear to cause issues on arm32. Sometimes we see OOMs.
In particular there is a concern that the thread that creates threads + the actual threads may starve the main thread, thus arbitrarily prolonging the scenario.

Thie fix tries to limit the total number of threads that the test creates, making its completion more deterministic.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[VSadov]

I've rebased/rerun the CI on this PR several times and did not see the issue reproducing. I think this is a sufficient fix for the test issue.

[Copilot]

Pull Request Overview

This PR improves the reliability and performance of the TestAnotherThread test method in the GC.GetTotalAllocatedBytes test suite.

• Adds an upper bound to the background task's loop to prevent potential infinite loops
• Reduces main thread iterations from 1000 to 100 for faster test execution while maintaining adequate coverage
• Maintains early termination capability when the test completes

[agocke]

Lgtm

[VSadov]

Thanks!