Unify handling of Lincheck TestThread and user threads in ManagedStrategy

[eupp]

Currently, there are several places in the ManagedStrategy class, where there is special handling of TestThread objects created by Lincheck, comparing with custom user created threads:

lincheck/src/jvm/main/org/jetbrains/kotlinx/lincheck/strategy/managed/ManagedStrategy.kt

Line 495 in f2011d4

if (thread is TestThread) return

Let's unify the logic for the two cases.