chore: update version to 5.3.1-SNAPSHOT (#3227) #6605

Job	Run time
sample_operators_tests (sample-operators/mysql-schema)	3m 16s
sample_operators_tests (sample-operators/metrics-processing)	18m 20s
sample_operators_tests (sample-operators/leader-election)	3m 53s
sample_operators_tests (sample-operators/tomcat-operator)	3m 33s
sample_operators_tests (sample-operators/webpage)	3m 47s
	32m 49s

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