Fix group query by using queryset instead of object

(cherry picked from commit abcbda53)

aleksis/core/schema/group.py

@@ -34,7 +34,7 @@ class GroupType(DjangoObjectType):
         if has_person(info.context.user) and [
             m for m in root.members.all() if m.pk == info.context.user.person.pk
         ]:
-            persons = (persons | Person.objects.get(pk=info.context.user.person.pk)).distinct()
+            persons = (persons | Person.objects.filter(pk=info.context.user.person.pk)).distinct()
         return persons
 
     @staticmethod
@@ -43,7 +43,7 @@ class GroupType(DjangoObjectType):
         if has_person(info.context.user) and [
             o for o in root.owners.all() if o.pk == info.context.user.person.pk
         ]:
-            persons = (persons | Person.objects.get(pk=info.context.user.person.pk)).distinct()
+            persons = (persons | Person.objects.filter(pk=info.context.user.person.pk)).distinct()
         return persons
 
     @staticmethod