print throws error with "flush" argument

Just ran across this on  CLUE (nrf52840)
using the "flush" argument for print throws an error

```
Adafruit CircuitPython 7.0.0-alpha.2-527-g47947dc23 on 2021-05-13; Adafruit CLUE nRF52840 Express with nRF52840
>>> print("hi",flush=True)
hi
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 22] Invalid argument
>>> 
```
