Fix possible notification loop (EXPOSUREAPP-4036) (#1750)

* Adding missing log tags, otherwise displays "BaseContinuationImpl" etc.

* Remember the last risk level result for which we did a change check.
This fixed the issue that if no new risk level calculation happened, and the last one triggered a notification,
killing and restarting the app would also trigger a notification.

Co-authored-by: Ralf Gehrer <ralfgehrer@users.noreply.github.com>
Co-authored-by: BMItter <46747780+BMItter@users.noreply.github.com>