Update xiao rp2040 pins

[prplz]

The schematic on the seeed website is incorrect/outdated. In reality there's an RGB LED connected to the pins as specified in this PR.
Tested on real hardware.

[Neradoc]

If these are the components of an RGB LED, and not independent "red LED", "green LED" and "blue LED", I believe it is customary to call the components LED_R, LED_G, LED_B (or possibly LED_RED, LED_GREEN, LED_BLUE). There doesn't seem to be strong conventions though. This is how it's done on the Pimoroni Tinny 2040 for example:

circuitpython/ports/raspberrypi/boards/pimoroni_tiny2040/pins.c

Lines 15 to 17 in 8eee16c

	{ MP_ROM_QSTR(MP_QSTR_LED_R), MP_ROM_PTR(&pin_GPIO18) },
	{ MP_ROM_QSTR(MP_QSTR_LED_G), MP_ROM_PTR(&pin_GPIO19) },
	{ MP_ROM_QSTR(MP_QSTR_LED_B), MP_ROM_PTR(&pin_GPIO20) },

[dhalbert]

@prplz could you checkout 7.1.x instead and submit a new PR against that branch? Then it will get in the 7.1.0 beta series. Thank you.

[prplz]

Oops, force push made stuff go a little weird.