The prepare scripts uses 'reg' to verify we're not going to
overwrite an existing image. The 'reg' command is not
available in Fedora 43. Use 'skopeo' instead. Skopeo
is part of the podman ecosystem so hopefully will live longer.
Fixes#27178.
Closesscylladb/scylladb#27179
(cherry picked from commit d6ef5967ef)
Closesscylladb/scylladb#27196