Update phpunit/phpunit requirement from ^9.6 to ^13.4 - #17

Process completed with exit code 2.

Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^13.4 -> satisfiable by phpunit/phpunit[13.4.4, ..., 13.5.x-dev]. - phpunit/phpunit[13.4.4, ..., 13.5.x-dev] require php >=8.4.1 -> your php version (7.4.33) does not satisfy that requirement.