More AssertionErrors from replication_notifier

[richvdh]

we have a function db_query_to_update_function which wraps a database query function so that it can be used as an update_function for replication streams. It relies on the wrapped function returning no more than the number of rows asked for. #7337 found and fixed one instance where this was not the case, but we should check if there are any more.

[richvdh]

as per #7351 (comment), at least the federation and account_data streams are broken. I think we should just go through each of the streams and check their behaviour, before this stuff bites us again.

[babolivier]

Removing the release blocker label as #7378 mitigates it, though I'm leaving this issue open as it looks like it needs more investigation.