Always fails with:

Downloading gha-serial: http://lightsandshapes.com/gha-serial
##[error]Unexpected HTTP response: 404

lightsandshapes.com being the website of papertigers. So looks like he removed that file GitHub Actions needs (it's not referenced in the repo, not sure where it gets any of that from).

I removed it for now, but should add it back: maybe as a fork or use something else.

FYI @nshalman @papertigers