[3.14] gh-149410: Test that typing.NoDefault is final (GH-149411) (#149419)

gh-149410: Test that `typing.NoDefault` is final (GH-149411)
(cherry picked from commit bad9296)

Co-authored-by: sobolevn <mail@sobolevn.me>

Author: miss-islington

Lib/test/test_typing.py

@@ -10859,6 +10859,10 @@ def test_no_attributes(self):
         with self.assertRaises(AttributeError):
             type(NoDefault).foo
 
+    def test_no_subclassing(self):
+        with self.assertRaises(TypeError):
+            class Test(type(NoDefault)): ...
+
 
 class AllTests(BaseTestCase):
     """Tests for __all__."""