docs: Tweak favicon setting so sphinx doesn't give an error locally.
docs: Tweak favicon setting so sphinx doesn't give an error locally.

adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython