Fix preference name

aleksis/apps/untis/util/mysql/importers/lessons.py

@@ -144,7 +144,7 @@ def import_lessons(
                 changed = False
                 is_primary_source = is_untis_primary_source(core_models.Group)
                 create_if_not_primary = get_site_preferences()[
-                    "untis_mysql__is_primary_source = is_untis_primary_source(Group)"
+                    "untis_mysql__create_objects_untis_not_primary_source"
                 ]
                 if not course_group and (is_primary_source or create_if_not_primary):