oc adm release mirror removes the architecture information

Issue

• When running the following command the architecture information is missing:

./oc adm release mirror -a ${LOCAL_SECRET_JSON} --to-dir=./removable-registry quay.io/openshift-release-dev/ocp-release:4.6.0-fc.5-x86_64
info: Mirroring 121 images to file://openshift/release ...
<dir>
[...]
 manifests:
      sha256:007637513a06eebb324561d234d64b9dc614adcb1c79b4efb3e9818bea09b108 -> 4.6.0-fc.5-ironic-inspector
      sha256:010737a642e6da90ac55edeb1aebe1e308dda607561cf04b2b9085d7277c0cd0 -> 4.6.0-fc.5-ironic-machine-os-downloader
      sha256:01a8e4ac77a3f534adfb8a3174b8d30ea63065aa5370f8f3f92446e46a8130a8 -> 4.6.0-fc.5-docker-registry
      sha256:0489c92a0845a2330062c4f10e45a5dcdc8b6d7982ea41c5b7e5485960943be9 -> 4.6.0-fc.5-pod
      sha256:058f695f28fa5cd43f98bbb4b187d3ce8d37f24771e43834bd5a119b4e3ff0a2 -> 4.6.0-fc.5-cli-artifacts
[...]