chore: update version to 5.3.1-SNAPSHOT #6604

Job	Run time
sample_operators_tests (sample-operators/webpage)	3m 20s
sample_operators_tests (sample-operators/tomcat-operator)	3m 23s
sample_operators_tests (sample-operators/metrics-processing)	18m 33s
sample_operators_tests (sample-operators/mysql-schema)	3m 8s
sample_operators_tests (sample-operators/leader-election)	3m 52s
	32m 16s

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