Your requirements could not be resolved to an installable set of packages.
Problem 1
- Root composer.json requires phpstan/phpstan ^1.11 -> satisfiable by phpstan/phpstan[1.11.0, ..., 1.11.9].
- phpstan/phpstan[1.11.0, ..., 1.11.9] require php ^7.2|^8.0 -> your php version (5.6.40) does not satisfy that requirement.