[Bug Report] Testing Qt notifications doesn't display any notification

### Describe the bug:

In Preferences -> UI -> Desktop notifications, select Use Qt, then click Test. Nothing happens.

- OpenSnitch version: 1.8.0
- OS version: Ubuntu 26.04
- Window Manager: KDE Wayland
- Kernel version: `Linux 7.0.0-15-generic #15-Ubuntu SMP PREEMPT_DYNAMIC Wed Apr 22 16:06:43 UTC 2026 x86_64 GNU/Linux`

### Additional context:

Notifications do appear after the pop-up timer runs out:

They also correctly end up in the list of notifications (which System notifications don't do):

So it seems that only testing is broken.