Fix: update namespace import for DependencyInjection\Extension

[fab987654321]

This PR fixes a Symfony 7.1 deprecation by using the recommended Extension class

Context

Since Symfony 7.1, the class Symfony\Component\HttpKernel\DependencyInjection\Extension is considered internal and will be deprecated in Symfony 8.1.

Using this class from EcPhp\CasBundle\DependencyInjection\CasExtension
triggers the following deprecation notice:

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.

[drupol]

Thank you, incorporated in version 3.0.5.