fix(WCOW): fix file access failure for multistage builds #4338

Job	Run time
prepare	1s
test / prepare	1m 45s
test / run (containerd, ./frontend/dockerfile, integration)	4m 56s
test / run (containerd, ./frontend/dockerfile, dockerfile)	6m 34s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	4m 37s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	6m 52s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	4m 30s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	6m 38s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 59s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	6m 38s
test / run (oci, ./frontend/dockerfile, integration)	4m 9s
test / run (oci, ./frontend/dockerfile, dockerfile)	5m 23s
test / run (oci-rootless, ./frontend/dockerfile, integration)	4m 34s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	5m 33s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	4m 36s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	5m 31s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 33s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	5m 59s
image (mainline)	4m 59s
image (labs)	5m 0s
scout	0s
release	0s
	1h 37m 47s

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