reduce amount of magic values, goal is to have specific states -> e.g. cancelled

src/model/notification.rs

@@ -278,7 +278,7 @@ mod test {
         let cancel_update = EventUpdate {
             name: &event.name,
             planned_amount_cox: event.planned_amount_cox as i32,
-            max_people: 0,
+            max_people: -1,
             notes: event.notes.as_deref(),
             always_show: event.always_show,
             is_locked: event.is_locked,