Incorporate fixes from https://github.com/micropython/micropython/pull/8459

[dhalbert]

• extmod/uasyncio: fix gather cancellation and handling of exceptions micropython/micropython#8459

[jepler]

This is partially done in #30 but was incomplete.

[kbsriram]

I could be wrong, but should this bug be closed? I wasn't able to spot any changes from the original commit that aren't either in this library or the core. Maybe the remaining changes intended (adding tests to circuitpython core?) made its way there as part of adafruit/circuitpython#8281 ?

[dhalbert]

@kbsriram I think you're right, since we updated quite recently when we merged recent versions of MicroPython. Thanks!