Add example test to ensure fix works

This test will removed before merging.

linux_os/guide/system/accounts/accounts-physical/screen_locking/console_screen_locking/no_tmux_in_shells/tests/example.pass.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+if grep -q 'tmux\s*$' /etc/shells ; then
+	sed -i '/tmux\s*$/d' /etc/shells
+fi