feat: allow PHPUnit 11

[kubawerlos]

PHPUnit 11 requires phpunit/php-code-coverage:^11.0: https://github.com/sebastianbergmann/phpunit/blob/11.0.0/composer.json#L35

CI changes are made because:

• phpunit/php-code-coverage:^11.0 requires nikic/php-parser:^5.0
• the latest stable vimeo/psalm does not yet allow nikic/php-parser:^5.0.

[kubawerlos]

With a lot of magic I've managed to install PHPUnit 11, I have no idea the error would happen with a normal installation.

[Jean85]

Closing in favor of #230.