Fix filter query for groups

aleksis/apps/alsijil/model_extensions.py

@@ -102,7 +102,7 @@ def annotate_person_statistics_for_school_term(
         datetime_end__date__lte=school_term.date_end,
     )
     if group:
-        documentations.filter(
+        documentations = documentations.filter(
             pk__in=Documentation.objects.filter(course__groups=group).union(
                 Documentation.objects.filter(course__groups__parent_groups=group)
             )