Use OpenShift 4.15.0-okd (#5000) #2403

Job	Run time
kurl-addon-changes-filter	4s
generate-tag	5s
build-kurl-proxy-melange-packages (ubuntu-20.04, amd64)	1m 51s
build-migrations-melange-packages (ubuntu-20.04, amd64)	3m 8s
build-kurl-proxy-melange-packages (arm64-runner-set, arm64)	3m 1s
build-kotsadm-melange-packages (ubuntu-20.04, amd64)	6m 53s
build-migrations-melange-packages (arm64-runner-set, arm64)	5m 4s
build-web	3m 31s
build-kotsadm-melange-packages (arm64-runner-set, arm64)	6m 56s
generate-kots-release-notes-pr	3s
Run regression testing	0s
build-kurl-proxy	44s
build-kots	6m 11s
goreleaser	10m 24s
build-migrations	32s
build-kotsadm	40s
build-kotsadm-bundle	1m 40s
generate-kurl-addon	2m 17s
publish-kurl-addon	7s
validate-kurl-addon	18s
regression-test	0s
publish-pact-contracts	31s
build-airgap	1m 29s
	55m 29s

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