Your requirements could not be resolved to an installable set of packages.
Problem 1
- Root composer.json requires php >=7.4.0 but your php version (5.3.29) does not satisfy that requirement.
Problem 2
- phpunit/phpunit[9.6.0, ..., 9.6.20] require php >=7.3 -> your php version (5.3.29) does not satisfy that requirement.
- Root composer.json requires phpunit/phpunit ~9.6 -> satisfiable by phpunit/phpunit[9.6.0, ..., 9.6.20].