add staff remove & staff invite test

app/Policies/EventPolicy.php

@@ -53,7 +53,15 @@ class EventPolicy
      */
     public function update(User $user, Event $event)
     {
-        return $user->id == $event->user_id;
+        if($user->id == $event->user_id) {
+            return true;
+        } else {
+            $testedUser = $event->guests()->where('users.id', $user->id)->first();
+            if($testedUser !== null) {
+                return $testedUser->pivot->is_staff;
+            }
+        }
+        return false;
     }
 
     /**