[3.9] bpo-40939: Fix test_keyword for the old parser (GH-20814)

diff --git a/Lib/keyword.py b/Lib/keyword.py
index afc3db3..a4db67e 100644
--- a/Lib/keyword.py
+++ b/Lib/keyword.py
@@ -19,7 +19,7 @@
     'False',
     'None',
     'True',
-    '__new_parser__',
+    '__peg_parser__',
     'and',
     'as',
     'assert',