fix: restore show filtering in nested timeslot routes

The Timeslot no longer has a show attribute. It is exposed through timeslot.schedule.show instead.

program/views.py

@@ -732,7 +732,7 @@ class APITimeSlotViewSet(
     viewsets.GenericViewSet,
 ):
     ROUTE_FILTER_LOOKUPS = {
-        "show_pk": "show",
+        "show_pk": "schedule__show",
         "schedule_pk": "schedule",
     }