Resolve "Group types that are managed by some app (e.g. cursus' "school class") can't be selected as timetable group type"

Closes #245 (closed)

@hansegucker could you have a look?

aleksis/apps/chronos/managers.py

@@ -878,12 +878,10 @@ class LessonEventQuerySet(PolymorphicQuerySet):
 
     def for_participant(self, person: Union[int, Person]) -> "LessonEventQuerySet":
         """Get all lesson events the person participates in (including amends)."""
-        amended = self.filter(
-            Q(amended_by__isnull=False) | Q(groups__members=person)
-        ).values_list("amended_by__pk", flat=True)
-        return self.filter(
-            Q(groups__members=person) | Q(pk__in=amended)
-        ).distinct()
+        amended = self.filter(Q(amended_by__isnull=False) | Q(groups__members=person)).values_list(
+            "amended_by__pk", flat=True
+        )
+        return self.filter(Q(groups__members=person) | Q(pk__in=amended)).distinct()
 
     def for_group(self, group: Union[int, Group]) -> "LessonEventQuerySet":
         """Get all lesson events for a certain group (including amends/as parent group)."""