PHPUnit 12 compatibility

[haeber]

Is your feature request related to a problem? Please describe.
It's currently not possible to upgrade to PHPUnit 12 or higher because this library is still restricted to max. PHPUnit ^11.x

Describe the solution you'd like

• Add in composer.json PHPUnit ^12.x compatibility and solve code issues/deprecations related to this.

Describe alternatives you've considered

• Finding an alternative to this library.

Additional context

• nothing to add

[alexislefebvre]

Someone may try to do the same thing than for PHPUnit 11: https://github.com/liip/LiipFunctionalTestBundle/pull/641/files