Use unique dummy ids in coursebook documentations query

aleksis/apps/alsijil/models.py

@@ -535,7 +535,7 @@ class Documentation(CalendarEvent):
                 existing_documentations.first()
                 if (existing_documentations := (event_reference_obj := event["REFERENCE_OBJ"]).documentation.filter(datetime_start=event["DTSTART"].dt, datetime_end=event["DTEND"].dt)).exists() else
                 cls(
-                    pk=f"DUMMY:{event_reference_obj.id}",
+                    pk=f"DUMMY;{event_reference_obj.id};{event['DTSTART'].dt.isoformat()};{event['DTEND'].dt.isoformat()}",
                     lesson_event=event_reference_obj,
                     course=event_reference_obj.course,
                     subject=event_reference_obj.subject,