dockerfile: promote experimental linter rule #7238

Job	Run time
prepare	3s
test / prepare	2m 49s
test / run (containerd-1.7, ./frontend/dockerfile, integration)	6m 18s
test / run (containerd-2.0, ./frontend/dockerfile, dockerfile)	4m 10s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	7m 22s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	8m 19s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	6m 51s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	10m 5s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 48s
test / run (containerd, ./frontend/dockerfile, dockerfile)	9m 18s
test / run (oci-rootless, ./frontend/dockerfile, integration)	5m 41s
test / run (containerd-2.0, ./frontend/dockerfile, integration)	4m 3s
test / run (oci, ./frontend/dockerfile, dockerfile)	7m 10s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	7m 18s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	5m 50s
test / run (containerd-1.7, ./frontend/dockerfile, dockerfile)	8m 47s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	7m 45s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	6m 37s
test / run (oci, ./frontend/dockerfile, integration)	5m 29s
test / run (containerd, ./frontend/dockerfile, integration)	6m 20s
image (labs)	6m 47s
image (mainline)	6m 49s
scout	0s
release	0s
	2h 19m 39s

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