Disallow `ADD --checksum=<SUM> <GITSRC> <DST>` #3498

Job	Run time
prepare	1s
test / prepare	1m 49s
test / run (containerd, ./frontend/dockerfile, integration)	4m 27s
test / run (containerd, ./frontend/dockerfile, dockerfile)	6m 5s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	4m 56s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	5m 56s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	4m 23s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	6m 22s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 41s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	6m 19s
test / run (oci, ./frontend/dockerfile, integration)	4m 9s
test / run (oci, ./frontend/dockerfile, dockerfile)	5m 49s
test / run (oci-rootless, ./frontend/dockerfile, integration)	3m 57s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	5m 17s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	3m 57s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	5m 22s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 3s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	5m 18s
image (mainline)	4m 52s
image (labs)	5m 3s
release	0s
	1h 32m 46s

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