Fix permission checking

aleksis/apps/alsijil/util/predicates.py

@@ -312,7 +312,7 @@ def is_lesson_event_teacher(user: User, obj: LessonEvent):
     or a teacher of the course, if the lesson event has one.
     """
     if obj:
-        return obj.course and is_course_teacher(user, obj) or user.person in obj.all_teachers()
+        return obj.course and is_course_teacher(user, obj) or user.person in obj.all_teachers
     return False