Fixed random aggregation_regress test_more_more_more() failure

The cause was assuming that an unordered queryset returns the values
always in the same order.

tests/aggregation_regress/tests.py

@@ -581,6 +581,7 @@ class AggregationTests(TestCase):
             6
         )
 
+        # Note: intentionally no order_by(), that case needs tests, too.
         publishers = Publisher.objects.filter(id__in=[1, 2])
         self.assertEqual(
             sorted(p.name for p in publishers),
@@ -591,10 +592,15 @@ 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),