Fix a bug in EDU Typing handling in syncapi.

When a user's typing status times out, it must advance both the
Notifier and the EDUCache. This inconsistency meant that some Sytests
that only does a single `/sync` saw a returned event stream it didn't
expect (though empty), and failed.

In production, this likely just has the effect of adding extra load on
`/sync`, as the stream positions will resync the next time a user is
added or removed via API.

syncapi/consumers/eduserver_typing.go

@@ -74,6 +74,7 @@ func NewOutputTypingEventConsumer(
 func (s *OutputTypingEventConsumer) Start() error {
 	s.eduCache.SetTimeoutCallback(func(userID, roomID string, latestSyncPosition int64) {
 		pos := types.StreamPosition(latestSyncPosition)
+		s.stream.Advance(pos)
 		s.notifier.OnNewTyping(roomID, types.StreamingToken{TypingPosition: pos})
 	})
 	return s.typingConsumer.Start()