Migrate to GitHub actions

[kinow]

Describe exactly what you would like to see in an upcoming release

Hi, some time ago I mentioned GitHub Actions in a issue of Cylc Flow (link). Cylc Flow is the most complex project build we have in the Cylc organization.

GitHub actions has at least one advantage, the checkout time must be better I reckon. But I would like to experiment with GitHub actions, and see if others agree to move the other projects too (before we tackle issues like remote tests in Cylc UI).

Cylc UI is the project I am more familiar with, and have a better idea of how the build process works, and how long it normally takes.

Additional context

Our build in Travis CI for Cylc UI takes around ~7m 30s.

The first build at the top happened at the same time of another build on GitHub actions.

The build on GitHub actions took half the time of the build on Travis for the same PR, just 3m 41s .

Note, that I had not enabled cache. npm install normally takes a long time. It took almost 2 minutes to run npm install on GitHub infra.

Then I added two more commits. The first new commit was based on the actions docs for caching, using their npm example (without restore_keys, simply caching based on the package-lock.json hash). This commit took about the same time to build (1 second difference 3m 42s).

The second commit was to modify the badge, and also to verify how much faster it was after using caching. The build took 1m 37s 🎉 🎊 .

Finally, I pushed one more commit, to remove .travis.yml. Again, one second difference.

One downside is that GitHub actions is a newer product. I used it during the beta, and there were several features missing, the interface was also a bit buggy. But now after 2 months I think, there are lots of documentation. Apparently several users have adopted it already. It has pretty much the same functionality as Travis free for Open Source (not sure about $$$ plans). And also looks like their infrastructure is faster for builds, at least for builds of JS projects.

ps: the git clone in Travis took 1.01 seconds, and npm install 77.05 seconds. Same commands in GitHub actions took 2 seconds (weird, longer on GitHub? Or maybe that's because Travis does a --depth=50? Not sure what GitHub action does, we are using their default checkout action), and 19 seconds.

Pull requests welcome!