[1.5.x] Fixed qs ordering related randomly failing test

The failure wasn't present in 1.6+, so this is not a backpatch.

tests/regressiontests/aggregation_regress/tests.py

@@ -588,10 +588,15 @@ class AggregationTests(TestCase):
         )
 
         publishers = publishers.annotate(n_books=Count("book"))
+        sorted_publishers = sorted(publishers, key=lambda x: x.name)
         self.assertEqual(
-            publishers[0].n_books,
+            sorted_publishers[0].n_books,
             2
         )
+        self.assertEqual(
+            sorted_publishers[1].n_books,
+            1
+        )
 
         self.assertEqual(
             sorted(p.name for p in publishers),