Merge pull request #21537 from fengxue-IS/051-monitorEnter3

(v0.51.0) Fixes preparePinnedVirtualThreadForUnmount assertion

Author: babsingh

runtime/vm/ContinuationHelpers.cpp

@@ -995,6 +995,8 @@ preparePinnedVirtualThreadForUnmount(J9VMThread *currentThread, j9object_t syncO
 						if (lock == oldValue) {
 							/* CAS succeeded, we can proceed with using the inflated monitor. */
 							VM_ObjectMonitor::incrementCancelCounter(J9OBJECT_CLAZZ(currentThread, syncObj));
+							/* Either the lock is acquired or FLC bit set, safe to release the inflated monitor. */
+							omrthread_monitor_exit(monitor);
 
 							if (J9_FLATLOCK_OWNER(lock) == currentThread) {
 								/* Lock is acquired. */