Make menu operations always work with "Test" menu in the sample.

Make menu operations always work with "Test" menu in the sample.

Some tests in the "Menu" menu of the menu sample worked with the "Test" menu
while others used the last one ("Help" initially but possibly something else
if the test commands from "Menubar" menu were used).

Harmonize all menu commands to use the "Test" menu now.

See #12668.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66138 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775