Release hotfix 0.21.1

[dvdsk]

An incorrect example snug in, see #381 (comment)

I fixed it on main however lets hold off a few hours on releasing a hotfix to see if we can bundle in any other urgent fixes.

[roderickvd]

A couple of small PRs to be considered for v0.21.1:

• dep: restore upgrade to cpal 0.16 (#754) #765
• dep: bump hound, rstest, and update crates #766
• fix: various v0.21 cleanups #767

First and last ones in particular snuck through.
Middle one (updating crates) I suggest we put on the checklist before doing a v0.x release.

[dvdsk]

Middle one (updating crates) I suggest we put on the checklist before doing a v0.x release.

done

[dvdsk]

I'll release this now, if we find anything else that's urgent we will just make a second hotfix next week.

[dvdsk]

I've added a 0.21.x branch for future hotfixes