[3.9] Include soft keywords in keyword.py (GH-20877). (GH-20880)

(cherry picked from commit 78319e373d57cd4da67660f888aa7092efbd6f24)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
diff --git a/Lib/keyword.py b/Lib/keyword.py
index a4db67e..59fcfb0 100644
--- a/Lib/keyword.py
+++ b/Lib/keyword.py
@@ -13,7 +13,7 @@
 Alternatively, you can run 'make regen-keyword'.
 """
 
-__all__ = ["iskeyword", "kwlist"]
+__all__ = ["iskeyword", "issoftkeyword", "kwlist", "softkwlist"]
 
 kwlist = [
     'False',
@@ -54,4 +54,9 @@
     'yield'
 ]
 
+softkwlist = [
+
+]
+
 iskeyword = frozenset(kwlist).__contains__
+issoftkeyword = frozenset(softkwlist).__contains__