Detect Que schema version missing due to bug in Rails schema dump - affects all versions of Rails 7 prior to 7.0.3

[ZimbiX]

See #363 (comment).

I reckon we should add some code to detect this at startup and warn/raise.

It could be possible to automatically detect which version of the schema we're migrated to in order to populate the missing comment automatically, but we'd have to maintain that with each new migration version. I don't think that's sustainable, and would defeat the purpose of recording the schema version anyway.

This could probably be addressed at the same time as #375.