Support OS version in platform string #5199

Job	Run time
prepare	1s
test / prepare	2m 0s
test / run (containerd, ./frontend/dockerfile, integration)	5m 30s
test / run (containerd, ./frontend/dockerfile, dockerfile)	7m 1s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	5m 5s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	6m 53s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	5m 5s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	7m 3s
test / run (containerd-1.7, ./frontend/dockerfile, integration)	5m 3s
test / run (containerd-1.7, ./frontend/dockerfile, dockerfile)	7m 38s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 29s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	9m 18s
test / run (oci, ./frontend/dockerfile, integration)	4m 30s
test / run (oci, ./frontend/dockerfile, dockerfile)	6m 27s
test / run (oci-rootless, ./frontend/dockerfile, integration)	4m 25s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	6m 5s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	4m 31s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	6m 8s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 7s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	5m 59s
image (mainline)	5m 52s
image (labs)	5m 29s
release	0s
scout	0s
	2h 0m 39s

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