Fix migration issue with affecting_time_spans creation

`affecting_time_spans` creation depends on `reservation_unit_hierarchy`
being created first, so we need to indicate this as a dependency in
the migration file.

reservations/migrations/0073_affectingtimespan.py

@@ -7,6 +7,7 @@
 
 class Migration(migrations.Migration):
     dependencies = [
+        ("reservation_units", "0102_create_reservation_unit_hierarchy_materialized_view"),
         ("reservations", "0072_alter_reservation_begin_alter_reservation_end"),
     ]