bpo-37151: simplify classmethoddescr_call (GH-13340)

diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 6b018cc..301a2d2 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -1613,8 +1613,8 @@
             spam_cm(spam.spamlist())
         self.assertEqual(
             str(cm.exception),
-            "descriptor 'classmeth' requires a type "
-            "but received a 'xxsubtype.spamlist' instance")
+            "descriptor 'classmeth' for type 'xxsubtype.spamlist' "
+            "needs a type, not a 'xxsubtype.spamlist' as arg 2")
 
         with self.assertRaises(TypeError) as cm:
             spam_cm(list)