Fixed #28152 -- Made migrations serialize sets as set literals rather than set().

tests/migrations/test_migrations_initial_false/0001_not_initial.py

@@ -25,6 +25,6 @@ class Migration(migrations.Migration):
         ),
         migrations.AlterUniqueTogether(
             name='author',
-            unique_together=set([('name', 'slug')]),
+            unique_together={('name', 'slug')},
         ),
     ]