Add macos-latest to CI matrix

[guilledk]

Accidentally bricked last PR... so here we go again.

[goodboy]

Hmm, the number of failures on that makes me think maybe we have something simple, maybe at syntax or import level that's broken.

Not sure what offhand since the runs hang 😂

Hopefully we'll get some OS X fanz to checkout it out eventually.

[goodboy]

@guilledk for fun you should bump this to latest master to see if the deterministic cancel stuff improves anything. I got my doubts though.

[goodboy]

@guilledk can we get this rebased? I got someone lookin to hack on the os x support.

[goodboy]

Replaced by #342