Fix CI (and switch to Github actions?)

[nabadger]

I've noticed the CI is broken (see #65 )

This might be a good opportunity to review the CI, and also switch to Github actions - main reason for this is that no one is really managing the Travis/Circle integrations from a user-management/accounts point of view.

Github actions would at least get rid of this problem, and I suspect over time integrate nicer with Github's UI.

We use it on some of our Github repos already (SRE team is gradually migration towards it and away from CircleCI for public repos).

https://docs.github.com/en/free-pro-team@latest/actions

[nabadger]

Upstream already switched to github-actions - we'll get this for free, but anything custom will be done as part of build-harness-extensions...