there return of a read operation that times out with no data received
is inconsistent:
```
Adafruit CircuitPython 7.3.0-beta.1-31-g73f6b4867-dirty on 2022-04-30; Adafruit Feather RP2040 with rp2040
>>>
>>> import board, busio
>>> print(board.UART().read(5))
None
Adafruit CircuitPython 6.3.0 on 2021-06-01; FeatherS2 with ESP32S2
>>> import board,busio
>>> print(board.UART().read(5))
None
Adafruit CircuitPython 7.3.0-beta.1 on 2022-04-07; Adafruit Feather STM32F405 Express with STM32F405RG
>>> import board, busio
>>> print(board.UART().read(5))
None
Adafruit CircuitPython 7.3.0-beta.1-31-g73f6b4867-dirty on 2022-04-28; Teensy 4.1 with IMXRT1062DVJ6A
>>> import board, busio
>>> print(board.UART().read(5))
b''
```
Since I have a PR on this file anyway, I thought I would put in the change to make it consistent
with the other 3 board types I tried. Can not say about any of the others.
6378343bb3