`updateMany` return type is wrong when `returning` is undefined

[aleclarson]

Fixing this will require access to the driver's QueryResultHKT type (AKA the RunResult type in SQLite).

That either means:

• adding it to the RelationalQueryBuilder type parameters (unlikely, since it's meant to be a readonly API).
• or introduce a db.mutate (or db.write?) namespace for the upsert, updateMany, create methods, instead of exposing them on db.query.