Rooms with custom notification rules get black square for notification icon

### Steps to reproduce

1. Set custom notification options for a room that don't match any of the 4 options in the menu (eg. `curl -X PUT --data-binary '{"actions": ["notify"]}' -H 'Authorization: Bearer [token goes here]' 'https://matrix.org/_matrix/client/v3/pushrules/global/room/[room ID]'`)
2. Hover over the room tile in the left panel in Element

### Outcome

#### What did you expect?
Not sure - the icon appears on hover to represent the current notification state, but since it's none of the 4 options in the menu, there's no obvious icon to display.

#### What happened instead?
Notifications icon is a black square because the black background gets set but none of the icon css classes get applied so no mask image.

### Operating system

macOS

### Application version

Nightly

### How did you install the app?

_No response_

### Homeserver

_No response_

### Will you send logs?

No