fields extension not compatible when model_validation is enabled for /collections endpoints

[alukach]

If model_validation is enabled, the outgoing response will fail validation when the fields extension makes a request for a partial record.

Not sure if this is something that necessarily needs to be fixed, however it feels worthy of logging.

[vincentsarago]

I'm pretty sure this is tested in the tests 🤔

I think you are specially talking about /collections and /collections/{collection_id} endpoints, so I edited the issue title