Bump version to 5.3.0 #238

Job	Run time
check / editor-config	9s
check / clang-checks	1m 37s
build-os-matrix	4s
build (oraclelinux:9) / build	2m 8s
rpm-build (oraclelinux:9) / rpm-build	5m 55s
make-tests (oraclelinux:9) / tests	1m 50s
ipfix-elements-check / ipfix-elements-checks	42s
rpm-install (oraclelinux:9) / rpm-install	1m 18s
	13m 43s

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