Fixed #30651 -- Made __eq__() methods return NotImplemented for not implemented comparisons.

Changed __eq__ to return NotImplemented instead of False if compared to
an object of the same type, as is recommended by the Python data model
reference. Now these models can be compared to ANY (or other objects
with __eq__ overwritten) without returning False automatically.

tests/prefetch_related/tests.py

@@ -1,3 +1,5 @@
+from unittest import mock
+
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ObjectDoesNotExist
 from django.db import connection
@@ -243,6 +245,7 @@ class PrefetchRelatedTests(TestDataMixin, TestCase):
         prefetch_1 = Prefetch('authors', queryset=Author.objects.all())
         prefetch_2 = Prefetch('books', queryset=Book.objects.all())
         self.assertEqual(prefetch_1, prefetch_1)
+        self.assertEqual(prefetch_1, mock.ANY)
         self.assertNotEqual(prefetch_1, prefetch_2)
 
     def test_forward_m2m_to_attr_conflict(self):