Fixed #26916 -- Fixed prefetch_related when using a cached_property as to_attr.

Thanks Trac alias karyon for the report and Tim for the review.

tests/prefetch_related/tests.py

@@ -743,6 +743,17 @@ class CustomPrefetchTests(TestCase):
         ).get(pk=self.house3.pk)
         self.assertIsInstance(house.rooms.all(), QuerySet)
 
+    def test_to_attr_cached_property(self):
+        persons = Person.objects.prefetch_related(
+            Prefetch('houses', House.objects.all(), to_attr='cached_all_houses'),
+        )
+        for person in persons:
+            # To bypass caching at the related descriptor level, don't use
+            # person.houses.all() here.
+            all_houses = list(House.objects.filter(occupants=person))
+            with self.assertNumQueries(0):
+                self.assertEqual(person.cached_all_houses, all_houses)
+
 
 class DefaultManagerTests(TestCase):