INT-3483: Fix `AbstractCorrelatingMH` deadlock

JIRA: https://jira.spring.io/browse/INT-3483

**Cherry-pick to 4.0.x & 3.0.x**
Roger that!
`endsWith` is a bad sample, through, because `Mockito.endsWith` returns `String`, but `assertThat` requires `Matcher`. So, only `Matchers.endsWith` is appropriate.
Does SF team know XD preferences?

Out of topic: I've checked `.unlock();` throughout the project. Only this bad place of usage.