UniGetUI v2026.1.9+ does not close on shutdown request

### Please confirm these before moving forward

- [x] I have searched for my issue and have not found a work-in-progress/duplicate/resolved issue.
- [x] I have tested that this issue has not been fixed in the latest [(beta or stable) release](https://github.com/Devolutions/UniGetUI/releases/).
- [x] I have checked the [FAQ](https://github.com/Devolutions/UniGetUI#frequently-asked-questions) section for solutions.
- [x] This issue is about a bug (if it is not, please use the [correct template](https://github.com/Devolutions/UniGetUI/issues/new/choose)).

### UniGetUI Version

v2026.1.9 onwards

### Windows version, edition, and architecture

Windows 10 an Windows 11

### Describe your issue

UniGetUI v2026.1.9+ does not close on shutdown request if using Avalonia is active.

### Steps to reproduce the issue

1. Install UniGetUI v2026.1.9 or UniGetUI v2026.1.10, have some package managers active.
2. Switch to new Avalonia UI.
3. Then shutdown having UniGetUI open.
4. UniGetUI will block shutting down, because it ignores the shutdown event, if Avalonia UI is active. It does not ignore shutdown, if classic UI is active.

### UniGetUI Log

```text
Not available. But nothing reported. UniGetUI just ignores shutdown if Avalonia UI is active.
```

### Package Managers Logs

```text
N.A.
```

### Relevant information

Shutdown is ignored, if Avalonia UI is active, blocking shutdown as requested from SCCM or other mechanisms, as long as shutdown is not forced.

### Screenshots and videos

_No response_