[3.6] bpo-31502: IDLE Configdialog again deletes custom themes and keysets. (GH-3634) (#3636)

This reverses a never-released regression resulting from bpo-31287.
(cherry picked from commit 0efc7c67)

Lib/idlelib/configdialog.py

@@ -1237,7 +1237,7 @@ class HighPage(Frame):
 
     def askyesno(self, *args, **kwargs):
         # Make testing easier.  Could change implementation.
-        messagebox.askyesno(*args, **kwargs)
+        return messagebox.askyesno(*args, **kwargs)
 
     def delete_custom(self):
         """Handle event to delete custom theme.
@@ -1683,7 +1683,7 @@ class KeysPage(Frame):
 
     def askyesno(self, *args, **kwargs):
         # Make testing easier.  Could change implementation.
-        messagebox.askyesno(*args, **kwargs)
+        return messagebox.askyesno(*args, **kwargs)
 
     def delete_custom_keys(self):
         """Handle event to delete a custom key set.