build: create an alias for php

[f15u]

This adds an alias for php.

It was already done in #58, but removed in d764e5c.

Some tools expects to have php available, eg. composer.

[TrafeX]

Hi @f15u,

Thank you! Based on the PHP version, this symlink is provided by the PHP packages in Alpine Linux.
It's probably in the PHP8.3 packages, but not in the PHP8.4 packages. So this patch is indeed needed!