541064a95b
The only (transitive) caller that seems to be interested in the format is the API endpoint for content listing. The warning about not being able to query in the expected format might not be seen by consumers that only use the API result, so this helps admins detect such images. It is also for future-proofing, should any new callers want to use only images of certain formats to error out early. Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>