Sets priority for this.
Priority controls how the toast behaves when another toast is already being displayed.
If priority is [enum@Adw.ToastPriority.normal], the toast will be queued.
If priority is [enum@Adw.ToastPriority.high], the toast will be displayed immediately, pushing the previous toast into the
queue instead.
| this |
a toast |
| priority |
the priority |