[s3 cache] Fix upload of downloaded layer #5273

Job	Run time
prepare	1s
test / prepare	2m 21s
test / run (containerd, ./frontend/dockerfile, integration)	1m 0s
test / run (containerd, ./frontend/dockerfile, dockerfile)	1m 9s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	55s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	55s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	55s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	54s
test / run (containerd-1.7, ./frontend/dockerfile, integration)	57s
test / run (containerd-1.7, ./frontend/dockerfile, dockerfile)	59s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	55s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	57s
test / run (oci, ./frontend/dockerfile, integration)	56s
test / run (oci, ./frontend/dockerfile, dockerfile)	54s
test / run (oci-rootless, ./frontend/dockerfile, integration)	54s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	56s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	53s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	56s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	56s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	55s
image	1s
release	1s
scout	1s
	19m 21s

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