Resolve "Check permission rules if they handle lessons with substitutions correctly"

Closes #147 (closed)

get_teachers will return the following:

• simply the teachers for events and extra lessons
• the original teachers for lesson periods without substitution, otherwise the new teacher

So, we have to check the teachers of lesson periods additionally to keep the access for the original teacher.

aleksis/apps/alsijil/util/predicates.py

@@ -26,8 +26,7 @@ def is_lesson_teacher(user: User, obj: Union[LessonPeriod, Event, ExtraLesson])
     in the lesson or the substitution linked to the given LessonPeriod.
     """
     if obj:
-        sub = obj.get_substitution() if isinstance(obj, LessonPeriod) else None
-        if sub and sub in user.person.lesson_substitutions.all():
+        if isinstance(obj, LessonPeriod) and user.person in obj.lesson.teachers.all():
             return True
         return user.person in obj.get_teachers().all()
     return False
@@ -212,16 +211,13 @@ def is_personal_note_lesson_teacher(user: User, obj: PersonalNote) -> bool:
     in the lesson or the substitution linked to the LessonPeriod of the given PersonalNote.
     """
     if hasattr(obj, "register_object"):
-        if getattr(obj, "lesson_period", None):
-            sub = obj.lesson_period.get_substitution()
-            if sub and user.person in Person.objects.filter(
-                lesson_substitutions=obj.lesson_period.get_substitution()
-            ):
-                return True
+        if (
+            isinstance(obj.register_object, LessonPeriod)
+            and user.person in obj.lesson_period.lesson.teachers.all()
+        ):
+            return True
 
         return user.person in obj.register_object.get_teachers().all()
-
-        return False
     return False