Fixed #33984 -- Reverted "Fixed #32980 -- Made models cache related managers."

This reverts 4f8c7fd9d9 and adds
two regression tests:
- test_related_manager_refresh(), and
- test_create_copy_with_m2m().

Thanks joeli for the report.

tests/m2m_regress/tests.py

@@ -39,14 +39,6 @@ class M2MRegressionTests(TestCase):
         self.assertSequenceEqual(e1.topics.all(), [t1])
         self.assertSequenceEqual(e1.related.all(), [t2])
 
-    def test_m2m_managers_reused(self):
-        s1 = SelfRefer.objects.create(name="s1")
-        e1 = Entry.objects.create(name="e1")
-        self.assertIs(s1.references, s1.references)
-        self.assertIs(s1.related, s1.related)
-        self.assertIs(e1.topics, e1.topics)
-        self.assertIs(e1.related, e1.related)
-
     def test_internal_related_name_not_in_error_msg(self):
         # The secret internal related names for self-referential many-to-many
         # fields shouldn't appear in the list when an error is made.
@@ -79,6 +71,20 @@ class M2MRegressionTests(TestCase):
         w.save()
         w.delete()
 
+    def test_create_copy_with_m2m(self):
+        t1 = Tag.objects.create(name="t1")
+        Entry.objects.create(name="e1")
+        entry = Entry.objects.first()
+        entry.topics.set([t1])
+        old_topics = entry.topics.all()
+        entry.pk = None
+        entry._state.adding = True
+        entry.save()
+        entry.topics.set(old_topics)
+        entry = Entry.objects.get(pk=entry.pk)
+        self.assertCountEqual(entry.topics.all(), old_topics)
+        self.assertSequenceEqual(entry.topics.all(), [t1])
+
     def test_add_m2m_with_base_class(self):
         # Regression for #11956 -- You can add an object to a m2m with the
         # base class without causing integrity errors