Migrate to GitHub Actions for CI testing.

[amcgregor]

The current version (5.4.1) as suggested in travis-ci/travis-ci#4756 is quite dated at this point. Problems have been encountered (relating to ABC metaclass usage) which may be resolved in subsequent (supported) releases. Depends on travis-ci/travis-ci#7507 upstream.

There is some hope, for example, utilizing nightly builds as per the recommendation of njs from #pypy on Freenode, ref:

• https://github.com/python-trio/trio/blob/master/.travis.yml
• https://github.com/python-trio/trio/blob/master/ci/travis.sh#L20

[njsmith]

For the record, I'm using nightly builds there because that project relies heavily on 3.5 features, and pypy's 3.5 support was still unreleased when I started, & is still in beta and under heavy development. It works pretty good but if I were targeting pypy2 then I'd probably use the latest release build from squeaky (as recommended by the official download page). Should pretty much just be a matter of changing the download URL.

I'm going to unsubscribe from this issue, so @ mention me if you want me to see replies. HTH, GL

[amcgregor]

Original IRC log: https://gist.github.com/amcgregor/69dc6d5d8169dd2fc9a89c5324a4a396

And an accidental close; wewt! Caffeine, how does it work?

[amcgregor]

Scratch that, new plan is to drop Travis-CI in favour of GitHub Actions. This likely will not result in the same level of coverage in terms of the build matrix (versions and combinations of installed features v. multiple MongoDB versions) but I'll see what I can pull off.