Your requirements could not be resolved to an installable set of packages.
Problem 1
- Root composer.json requires phpunit/phpunit 11.2.8 -> satisfiable by phpunit/phpunit[11.2.8].
- phpunit/phpunit 11.2.8 requires php >=8.2 -> your php version (7.3; overridden via config.platform, actual: 8.3.9) does not satisfy that requirement.