Use python convention

aleksis/apps/cursus/schema.py

@@ -203,8 +203,8 @@ class CreateSchoolGradeMutation(DjangoBatchCreateMutation):
         group_type, __ = GroupType.objects.managed_by_app(app_label).get_or_create(
             name=SCHOOL_GRADE_GROUP_TYPE_NAME, managed_by_app_label=app_label
         )
-        for schoolGrade in input:
-            schoolGrade["group_type"] = group_type.pk
+        for school_grade in input:
+            school_grade["group_type"] = group_type.pk
         return input