ListTranscriptions returns a 403 when an element is a folder

If this behavior is to be kept as it is, it should be a 400, and the frontend should avoid doing this. But should we keep this?

• An element being a folder does not imply it should not have a zone.
• Since we are getting rid of zones on transcriptions, nothing stops a transcription from being on an element without a zone now; that could be a feature.