Symfony Functional Test Case

This small patch fixes an issue that arises in Symfony 5.3, where the getContainer method in the parent class was made non-static; the same issue was encountered and resolved in the upstream project.

This new minor adds support for using the library with PHP 8.

This is finally the stable release of this forked library, and it only bumps the PHP requirement to PHP 7.2, everything else is the same.