bpo-40389: Improve repr of typing.Optional (#19714)

diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index e8fe455..b20103b 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -2028,7 +2028,7 @@
         class C:
             x: Union[int, type(None)] = None
 
-        self.assertDocStrEqual(C.__doc__, "C(x:Union[int, NoneType]=None)")
+        self.assertDocStrEqual(C.__doc__, "C(x:Optional[int]=None)")
 
     def test_docstring_list_field(self):
         @dataclass