[s3 cache] Fix upload of downloaded layer #5274

Job	Run time
prepare	1s
test / prepare	2m 24s
test / run (containerd, ./frontend/dockerfile, integration)	5m 42s
test / run (containerd, ./frontend/dockerfile, dockerfile)	16m 0s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	5m 11s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	15m 53s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	5m 27s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	9m 40s
test / run (containerd-1.7, ./frontend/dockerfile, integration)	5m 16s
test / run (containerd-1.7, ./frontend/dockerfile, dockerfile)	16m 41s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	6m 28s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	17m 39s
test / run (oci, ./frontend/dockerfile, integration)	4m 48s
test / run (oci, ./frontend/dockerfile, dockerfile)	16m 39s
test / run (oci-rootless, ./frontend/dockerfile, integration)	4m 49s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	15m 41s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	5m 24s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	16m 15s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 45s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	9m 49s
image (mainline)	5m 27s
image (labs)	5m 29s
release	0s
scout	0s
	3h 15m 28s

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