bpo-44566: resolve differences between asynccontextmanager and contextmanager (GH-27024) (#27266)

(cherry picked from commit 7f1c330da31c54e028dceaf3610877914c2a4497)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 453ef6c..e6500da 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -126,19 +126,22 @@ def woohoo():
         self.assertEqual(state, [1, 42, 999])
 
     def test_contextmanager_except_stopiter(self):
-        stop_exc = StopIteration('spam')
         @contextmanager
         def woohoo():
             yield
-        try:
-            with self.assertWarnsRegex(DeprecationWarning,
-                                       "StopIteration"):
-                with woohoo():
-                    raise stop_exc
-        except Exception as ex:
-            self.assertIs(ex, stop_exc)
-        else:
-            self.fail('StopIteration was suppressed')
+
+        class StopIterationSubclass(StopIteration):
+            pass
+
+        for stop_exc in (StopIteration('spam'), StopIterationSubclass('spam')):
+            with self.subTest(type=type(stop_exc)):
+                try:
+                    with woohoo():
+                        raise stop_exc
+                except Exception as ex:
+                    self.assertIs(ex, stop_exc)
+                else:
+                    self.fail(f'{stop_exc} was suppressed')
 
     def test_contextmanager_except_pep479(self):
         code = """\