Move from Travis CI to GitHub Actions

[HonkingGoose]

The Travis CI on the .org domain is shutting down very soon.
After the shutdown no tests will run on pushes to master or when PRs are opened that target master.

Travis suggest that you migrate to their offering on the .com domain. You get a one-time 1000 minutes of build time. After the free one time credit is used up, you can apply to open source plan where "upon validated request you may receive free OSS credits for your public builds".

Quote from https://www.travis-ci.com/plans

Free for open source. We love the Open Source Community, and to show how much we love it, upon validated request placed with our Support Team you may receive free OSS credits for your public builds.

I think the easiest thing is to migrate to GitHub Actions, as those are free for public repositories, with no strings attached.

GitHub docs on migrating from Travis to GitHub Actions

[pedrorijo91]

I think it may be easier just to ask for free credits. but if anyone wants to work on the migration for github actions it would be ok as well

cc @peff it seems we need an admin on this:

• https://github.com/marketplace/travis-ci/plan/MDIyOk1hcmtldHBsYWNlTGlzdGluZ1BsYW43MA==#pricing-and-setup
• https://docs.travis-ci.com/user/migrate/open-source-on-travis-ci-com/

[peff]

I'd rather move to Actions, as the experience seems better to me (I may be biased, though). Specifically, I've seen cases where the Travis jobs are queued for a half hour or more, which holds up further movement on a PR.

I also haven't found our tests to be all that helpful in general, as they really just render a couple of pages (and it looks like there's a ton of stale inactive tests, too!). They were helpful with the ruby/rails transition recently, but the vast majority of changes we do are in the rake jobs that pull in book and manpage content, and those aren't covered at all (good tests there would be quite a bit trickier, as it's a bit expensive to do a full import; we might be able to get by with a single static version or something).

[jnavila]

Plus we really need some reliable test (see #1561)