Support Symfony v6 (and Laravel v9)

This package does not work with a Laravel v9 application.
```
- Root composer.json requires code-lts/doctum ^5.5 -> satisfiable by code-lts/doctum[v5.5.0].
- laravel/framework[v9.0.0, ..., v9.1.0] require symfony/process ^6.0 -> satisfiable by symfony/process[v6.0.0, v6.0.2, v6.0.3].
- Conclusion: don't install symfony/process v6.0.3 (conflict analysis result)
```