Add workflow to build aphex for PHP 7.3 and 7.4
Add workflow to build aphex for PHP 7.3 and 7.4

As far as I can tell this works locally with nektos/act. We're using
Docker's official metadata-action to handle tagging the images, so it
should tag images with stuff like v8.1.2 or whatever automatically?

Anyway, I put the PHP version into the image name, instead of the
image's tag, which means that it can't possibly mess up the old Aphex
image from before. Nothing to worry about.

ethical-jobs/aphex