pull by digest of encrypted images fails trying to edit the manifest

ERROR: copy needs an updated manifest but that was known to be forbidden. "Destination specifies a digest"

```
podman build --squash-all --format oci --omit-history --layers -t me/image .
podman push -f oci --compression-format=zstd:chunked --encryption-key=jwe:/me/key me/image

podman pull --decryption-key=/me/keyp me/image@sha256:abc123
# error here
```