PHPUnit 10 Compatibility

[aik099]

Research what kind of effort is needed to make this project compatible with PHPUnit 10 (or even if that is possible).

Resources:

• https://github.com/Yoast/PHPUnit-Polyfills/releases/tag/2.0.0
• https://phpconference.com/blog/phpunit-10-all-you-need-to-know-about-the-latest-version/
• https://phpunit.de/announcements/phpunit-10.html