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/editor.py b/Lib/idlelib/editor.py
index 3f034f8..1a16389 100644
--- a/Lib/idlelib/editor.py
+++ b/Lib/idlelib/editor.py
@@ -267,7 +267,7 @@
         self.saved_change_hook()
         self.update_recent_files_list()
         self.load_extensions()
-        menu = self.menudict.get('windows')
+        menu = self.menudict.get('window')
         if menu:
             end = menu.index("end")
             if end is None:
@@ -410,7 +410,7 @@
         ("format", "F_ormat"),
         ("run", "_Run"),
         ("options", "_Options"),
-        ("windows", "_Window"),
+        ("window", "_Window"),
         ("help", "_Help"),
     ]
 
@@ -437,7 +437,7 @@
 
     def postwindowsmenu(self):
         # Only called when Window menu exists
-        menu = self.menudict['windows']
+        menu = self.menudict['window']
         end = menu.index("end")
         if end is None:
             end = -1