The `koji-osbuild` Hub schema has been relaxed a bit in the latest
release (v11). Adjust the schema in Pungi to reflect changes in
`koji-osbuild`.
For more information on the changes in `koji-osbuild`, see:
https://github.com/osbuild/koji-osbuild/pull/108
Signed-off-by: Tomáš Hozza <thozza@redhat.com>