disable yet another motd zincati upgrade warning

Test are currently failing because the next images introduced a new
warning regrading to their OCI image update which we don't care about.
So just disable it like the others.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

Author: Luap99

podman-image/00-podman-machine.preset

@@ -6,6 +6,7 @@ disable coreos-warn-invalid-mounts.service
 # We don't use zincati but because we ship our own custom builds so
 # we don't care about the coreos update migration to OCI images.
 disable coreos-oci-migration-motd.service
+disable coreos-container-signing-migration-motd.service
 
 # Disable coreos chrony config, we do provide our own.
 disable coreos-platform-chrony-config.service