[3.1.x] Fixed #31990 -- Fixed QuerySet.ordered for GROUP BY queries on models with Meta.ordering.

Regression in 0ddb4ebf7b.

Thanks Julien Dutriaux for the report.
Backport of e11d05e0b4 from master

django/db/models/query.py

@@ -1220,7 +1220,12 @@ class QuerySet:
             return True
         if self.query.extra_order_by or self.query.order_by:
             return True
-        elif self.query.default_ordering and self.query.get_meta().ordering:
+        elif (
+            self.query.default_ordering and
+            self.query.get_meta().ordering and
+            # A default ordering doesn't affect GROUP BY queries.
+            not self.query.group_by
+        ):
             return True
         else:
             return False

docs/releases/3.1.2.txt

@@ -11,3 +11,8 @@ Bugfixes
 
 * Fixed a bug in Django 3.1 where ``FileField`` instances with a callable
   storage were not correctly deconstructed (:ticket:`31941`).
+
+* Fixed a regression in Django 3.1 where the :attr:`.QuerySet.ordered`
+  attribute returned incorrectly ``True`` for ``GROUP BY`` queries (e.g.
+  ``.annotate().values()``) on models with ``Meta.ordering``. A model's
+  ``Meta.ordering`` doesn't affect such queries (:ticket:`31990`).

tests/queries/tests.py

@@ -2074,6 +2074,16 @@ class QuerysetOrderedTests(unittest.TestCase):
         self.assertIs(qs.ordered, False)
         self.assertIs(qs.order_by('num_notes').ordered, True)
 
+    def test_annotated_default_ordering(self):
+        qs = Tag.objects.annotate(num_notes=Count('pk'))
+        self.assertIs(qs.ordered, False)
+        self.assertIs(qs.order_by('name').ordered, True)
+
+    def test_annotated_values_default_ordering(self):
+        qs = Tag.objects.values('name').annotate(num_notes=Count('pk'))
+        self.assertIs(qs.ordered, False)
+        self.assertIs(qs.order_by('name').ordered, True)
+
 
 @skipUnlessDBFeature('allow_sliced_subqueries_with_in')
 class SubqueryTests(TestCase):