Update action to Node 16

[smoeding]

I'm using purcell/setup-emacs@master in a Github workflow and lately I'm seeing warnings about Node 12 deprecation.
It seems all actions need to update to Node 16:
https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/

Could you update your code accordingly? Thanks!

[purcell]

Fixed by #30, I believe.