Deprecated extension

[garak]

In Symfony 7.1:

The "Symfony\Component\HttpKernel\DependencyInjection\Extension" class is considered internal since Symfony 7.1, to be deprecated in 8.1; use Symfony\Component\DependencyInjection\Extension\Extension instead. It may change without further notice. You should not use it from "Beelab\Recaptcha2Bundle\DependencyInjection\BeelabRecaptcha2Extension".

In Symfony 6 the proper class is already present, so we can safely change our extension point and guarantee the maximum forward compatibility.
By the way, we can drop Symfony 6.3 and raise the minimum Symfony version to 6.4