improve: rename junit5 module to junit (#3081) #6030

Job	Run time
sample_operators_tests (sample-operators/mysql-schema)	2m 56s
sample_operators_tests (sample-operators/webpage)	3m 16s
sample_operators_tests (sample-operators/tomcat-operator)	3m 13s
sample_operators_tests (sample-operators/leader-election)	3m 35s
	13m 0s

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