Have keypad/numpad shortcuts appear correctly in dialog

In Xubuntu 20.04, window tiling is assigned to Super + Keypad [1..9], but appear in the dialog as Super + [1..9], which is confusing as Super + [1..4] are assigned in the Keyboard preferences dialog for various apps.

I propose that KP_[1..9] appear as 'Keypad [1..9]'.

https://github.com/Xubuntu/xubuntu-default-settings/blob/master/etc/xdg/xdg-xubuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml#L74