Auto-migrate PHPunit configuration

[jnoordsij]

Description

Auto-migrates PHPUnit configuration to match latest configuration scheme.

Motivation and Context

When running vendor/bin/phpunit with the current configuration, the package suggests to (automatically) migrate the configuration to the latest schema. This PR applies the auto-migration and slightly reworks the formatting in this file.

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.