Stuck notifications: Stuck notification after room upgrade

### Steps to reproduce

1. Be in a room set to 'Mentions Only'
2. Room is upgraded by another party
3. Join upgraded room by accepting invite from other party
4. Realize there is still a notification in the old room
5. Clear that from the banner
6. Suffer a `(1)` that keeps coming back despite local echo saying otherwise
7. Have someone else send an event
8. Read that event
9. Notification goes away

### Outcome

#### What did you expect?

Notifications to work.

#### What happened instead?

See above.

### Operating system

Windows 10

### Application version

Nightly

### How did you install the app?

The Internet

### Homeserver

t2l.io

### Will you send logs?

Yes