[Keyboard] enable RGB underglow on heckerboards/axon40 (#13490)

This PCB uses RGB underglow LEDs. If the user doesn't want them, they can turn them off with a keycode.

keyboards/checkerboards/axon40/rules.mk

@@ -17,6 +17,6 @@ SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
 # if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
 NKRO_ENABLE = yes           # USB Nkey Rollover
 BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
-RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
+RGBLIGHT_ENABLE = yes       # Enable keyboard RGB underglow
 BLUETOOTH_ENABLE = no       # Enable Bluetooth
 AUDIO_ENABLE = no           # Audio output