[Pusher] New notifications count increment doesnt work

### Current Behavior

Unread notifications count doesn't update on events

### Steps to Reproduce

1. Log-in (to be able to subscribe to private channel) and go to any page
2. Receive new pusher notification (post in discussion you are subscribed to; new private discussion; etc)
3. Notifications count doesnt update untill the page is refreshed

### Expected Behavior

Unread notifications count should increment by 1 with each notification

### Screenshots

_No response_

### Environment

- Flarum version: 1.8.3
- PHP version: 8.1

### Output of `php flarum info`

_No response_

### Possible Solution

https://github.com/flarum/framework/blob/1.x/extensions/pusher/js/src/forum/index.tsx#L152C12-L153C84

Replace in those 2 lines:
app.session.user.unreadNotificationCount() ?? 0 + 1 **to** (app.session.user.unreadNotificationCount() ?? 0) + 1
app.session.user.newNotificationCount() ?? 0 + 1 **to** (app.session.user.newNotificationCount() ?? 0) + 1

### Additional Context

_No response_