Fix get_teachers_short_names

aleksis/apps/alsijil/models.py

@@ -118,7 +118,7 @@ class Documentation(CalendarEvent):
             return self.course.groups.all()
 
     def get_teachers_short_names(self) -> List[str]:
-        return [teacher.short_name or teacher.name for teacher in self.teachers]
+        return [teacher.short_name or teacher.name for teacher in self.teachers.all()]
 
     def __str__(self) -> str:
         start_datetime = CalendarEvent.value_start_datetime(self)