Update readgpio_s3.py

[synco]

To be consistent with the processor example I'd expect this... not sure about the knock-on effects.

[wnienhaus]

Actually esp32s2 is the correct value even for the ESP32-S3, because it specifies the instruction set of the ULP, not the overall device. The ESP32-S2 and ESP32-S3 have an identical ULP (at least the FSM ULP) which is why we simply called it all "esp32s2".

I can see how that can be confusing though. The README refers to this: https://github.com/micropython/micropython-esp32-ulp#id1, but maybe it could be easier, if we supported esp32s3 as a cpu type and simply treat it the same as esp32s2 internally.