🍒 xkb: fix testing if on keypad
XKB_KEY_KP_9 is 0xffb9 while XKB_KEY_KP_Equal is 0xffbd and XKB_KEY_F1 is 0xffbe. So XKB_KEY_KP_Equal, instead of XKB_KEY_KP_9, has the maximum keysym for keypad keys.
(cherry picked from commit 681752ad)