Test Emacs version on GitHub Actions

What I did

Added the Emacs ERT tests to the GitHub Actions workflow, after TravisCI stopped working.

What happened

It complained with this error:

emacs: standard input is not a tty

What I wanted to happen

Run the way it used to on Travis.

Analysis

I found a bunch of actions to help:

• setup emacs
• emacs lisp check I haven't tried it yet, but it looks like it can run ERT.
• cask I used it on Travis, but I think it's not needed with setup emacs.
• There's some discussion on actions/runner#241. That's where I learned about script and scriptreplay.