Bump version to 5.3.0 #241

Job	Run time
check / editor-config	11s
check / clang-checks	1m 44s
build-os-matrix	2s
make-tests (oraclelinux:9) / tests	1m 46s
build (oraclelinux:9) / build	2m 3s
rpm-build (oraclelinux:9) / rpm-build	5m 41s
ipfix-elements-check / ipfix-elements-checks	43s
rpm-install (oraclelinux:9) / rpm-install	1m 21s
	13m 31s

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