Notification: ensure that a notification is displayed when a Push cannot be resolved.

Previously the error was logged and added to push history but no notification was shown, so the user fully miss the new message.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/notification/NotificationData.kt

@@ -68,6 +68,7 @@ sealed interface NotificationContent {
         ) : MessageLike
 
         data object RoomEncrypted : MessageLike
+        data object UnableToResolve : MessageLike
         data class RoomMessage(
             val senderId: UserId,
             val messageType: MessageType