Refactor TestContainerSchedulerQueuing.testContainerUpdateExecTypeGuaranteedToOpportunistic

In 3.x, TestContainerSchedulerQueuing.testContainerUpdateExecTypeGuaranteedToOpportunistic has redundant assertions. Since the UT throws timeout exception, GenericTestsUtils.waitFor() guarantees that the predicate is met successfully. Otherwise, the UT would throw a timeout exception.
The redundant loop causes confusion in understanding the test unit and may increase the possibility of failure in case the container terminates