Missing icon on notifications

### Describe the bug

On Linux, notifications get sent with an icon placeholder instead of Cinny app icon

### Reproduction

receive a notification
the toast has a placeholder icon

### Expected behavior

Receive notification
toast without app icon

### Platform and versions

```shell
elementary OS 8.1 (Ubuntu 24.04)
Cinny 4.10.0, installed from Flathub
```

### Additional context

_No response_