audio.play(wait=False) still blocks

Running this line on the REPL and the two sounds are played consecutively and blocking until they are both done:

```
MicroPython v1.13 on 2021-03-16; micro:bit v2.0.0-beta.5 with nRF52833
Type "help()" for more information.
>>> audio.play(Sound.TWINKLE, wait=False); audio.play(Sound.SAD, wait=False)
>>>
```