TestEagerReclaimHumongousRegionsClearMarkBits checks whether after eager reclaim during marking the mark on the humongous object is cleared correctly.

It does so with a trial-and-error approach allocating humongous objects and hoping that the faulty state somehow occurs.

This can take a long time, and although the test limits itself to 50s runtime, for some reason there can still be sporadic timeouts in some setups.

However for a long time it is possible to halt concurrent mark just before completion, inducing the exact state needed for this test. So rewrite the test to be more targeted.