bpo-33924: Change IDLE mainmenu.menudefs key 'windows' to 'window' (GH-7836)


Every other menudef key is the lowercase version of the
corresponding main menu entry (in this case, 'Window').
(cherry picked from commit 33c7420e7dd9d8e5b2aa15e98da6291bab6fcf33)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
diff --git a/Lib/idlelib/mainmenu.py b/Lib/idlelib/mainmenu.py
index 04acaed..9fe6b52 100644
--- a/Lib/idlelib/mainmenu.py
+++ b/Lib/idlelib/mainmenu.py
@@ -97,7 +97,7 @@
    ('_Code Context', '<<toggle-code-context>>'),
    ]),
 
- ('windows', [
+ ('window', [
    ('Zoom Height', '<<zoom-height>>'),
    ]),