Fix exception when updating summary notifications (#3976)

dc9e9f2
modifed the code that fetched the value of EXTRA_NOTIFICATION_TYPE in an
intent, to use getSerializable().

However, the value was being placed in to the intent using putString().

This caused an exception when trying to update the summary notification,
so it would never update.

```
java.lang.ClassCastException: java.lang.String cannot be cast to com.keylesspalace.tusky.entity.Notification$Type
    at com.keylesspalace.tusky.components.notifications.NotificationHelper.updateSummaryNotifications(NotificationHelper.java:321)
    at com.keylesspalace.tusky.components.notifications.NotificationFetcher.fetchAndShow(NotificationFetcher.kt:87)
    at com.keylesspalace.tusky.components.notifications.NotificationFetcher$fetchAndShow$1.invokeSuspend(Unknown Source:14)
```

Fix this by placing the value in to the intent using putSerializable(),
to match how it will be fetched.

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationHelper.java

@@ -238,7 +238,7 @@ public static android.app.Notification make(final Context context, NotificationM
         Bundle extras = new Bundle();
         // Add the sending account's name, so it can be used when summarising this notification
         extras.putString(EXTRA_ACCOUNT_NAME, body.getAccount().getName());
-        extras.putString(EXTRA_NOTIFICATION_TYPE, body.getType().toString());
+        extras.putSerializable(EXTRA_NOTIFICATION_TYPE, body.getType());
         builder.addExtras(extras);
 
         // Only alert for the first notification of a batch to avoid multiple alerts at once