ci: add GitHub Actions to integrate with GitHub more easily

[owenvoke]

This would be completely up to you, but it allows integrating directly with GitHub more easily. 🙂

For reference, you can see the builds on my repository. 👍🏻 Tests passing on PHP 7.3 to 8.1 (I added PHP 7.4 and 8.1)

[megahertz]

Thank you. Looks pretty nice, but I prefer not to use third-party actions which aren't well-known. I'm going to make a few changes and merge it a bit later.

[owenvoke]

No problem. 👍🏻