Migrate builds to GHA

[nulano]

Fixes #68

For python-pillow/Pillow#5028

The script is almost an exact copy from Travis, except updated to GHA syntax; there is just one small change due to file permissions: sudo chmod a+w . added at the start of the build and the sudo chown command moved later.

Docker login details need to be stored as a Github Secret in DOCKER_USERNAME and DOCKER_PASSWORD.

[hugovk]

(Consistency nits)

Thanks!

[hugovk]

For reference, example builds:

• Before: https://travis-ci.com/github/python-pillow/docker-images/builds/198202805
• After: https://github.com/nulano/docker-images/actions/runs/346077582

---

@wiredfool Please could you review and add the credentials as secrets?

• https://github.com/python-pillow/docker-images/settings/secrets

[nulano]

As a test/demonstration, I have also pushed the built images to my Docker account and tested here: https://github.com/nulano/Pillow/actions/runs/346068049/workflow#L44

[hugovk]

Let's merge and add credentials later. Thanks!

[wiredfool]

Sorry, this disappeared into my backlog, I’ll try to dig out the creds.