bpo-40939: Generate keyword.py using the new parser (GH-20800)

(cherry picked from commit 9727694f08cad4b019d2939224e3416312b1c0e1)

Co-authored-by: Lysandros Nikolaou <lisandrosnik@gmail.com>
diff --git a/Lib/keyword.py b/Lib/keyword.py
index ddcbb25..afc3db3 100644
--- a/Lib/keyword.py
+++ b/Lib/keyword.py
@@ -1,13 +1,14 @@
-"""Keywords (from "Grammar/Grammar")
+"""Keywords (from "Grammar/python.gram")
 
 This file is automatically generated; please don't muck it up!
 
 To update the symbols in this file, 'cd' to the top directory of
 the python source tree and run:
 
-    python3 -m Parser.pgen.keywordgen Grammar/Grammar \
-                                      Grammar/Tokens \
-                                      Lib/keyword.py
+    PYTHONPATH=Tools/peg_generator python3 -m pegen.keywordgen \
+        Grammar/Grammar \
+        Grammar/Tokens \
+        Lib/keyword.py
 
 Alternatively, you can run 'make regen-keyword'.
 """
@@ -18,6 +19,7 @@
     'False',
     'None',
     'True',
+    '__new_parser__',
     'and',
     'as',
     'assert',