Enable PHP 7.3 compat

This latest release for PHP 7.3.

It was made so that composer updates can be done on PHP 7.3 projects without problems. This release confirms that as of November 2024, it is possible to run composer create-projcet bear/skeleton on PHP 7.3 to install new projects.

This release is not intended to be practical, but to demonstrate the availability of BEAR.Sunday.