[Enum] reformat and add doc strings (GH-23705)

diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index f2171b5..ab4b52f 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -429,7 +429,7 @@ def red(self):
     def test_reserved__sunder_(self):
         with self.assertRaisesRegex(
                 ValueError,
-                '_sunder_ names, such as "_bad_", are reserved',
+                "_sunder_ names, such as '_bad_', are reserved",
             ):
             class Bad(Enum):
                 _bad_ = 1