Bump PHPUnit to 10

[FelixJacobi]

+ Update Faker to current version. Must be done in 6.0 since PHPUnit 10 does not support PHP 7.x anymore.

[samuelwei]

@FelixJacobi This should be done in 6.1?

[FelixJacobi]

Yes. To make things less complex and more predictable for library consumers, we're focusing on removing deprecated features in 6.0.