fix: mockito and OpenJDK warning when running tests (#3327) #6961

Job	Run time
sample_operators_tests (sample-operators/tomcat-operator)	2m 58s
sample_operators_tests (sample-operators/operations)	8m 33s
sample_operators_tests (sample-operators/webpage)	3m 34s
sample_operators_tests (sample-operators/mysql-schema)	3m 0s
sample_operators_tests (sample-operators/leader-election)	3m 27s
	21m 32s

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