[browser][MT] Some tests deadlock without -backgroundExec

[pavelsavara]

Without -backgroundExec and with I/O thread

AsyncEnumerableToBlockingEnumerableTests.AsyncEnumerableWithDelays
AsyncEnumerableToBlockingEnumerableTests.AsyncEnumerableWithException
AsyncEnumerableToBlockingEnumerableTests.AsyncEnumerableWithCancellation
TaskContinueWithTests.TestNoDeadlockOnContinueWith
TaskContinueWithTests.LongContinuationChain_Await_DoesNotStackOverflow
SemaphoreSlimTests.RunSemaphoreSlimTest1_WaitAsync_NegativeCases

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[pavelsavara]

this is maybe improved by #99836, let's test it again