[Symfony Bundle] Fix the usage of a deprecated class

[javiereguiluz]

Fixes this issue spotted while updating some app to 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 
"AsyncAws\Symfony\Bundle\DependencyInjection\AsyncAwsExtension".

[jderusse]

Hello, tests are failing. Could you please add an entry in the Symfony/Bundle changelog file?

[javiereguiluz]

Do we really need an entry in the changelog? The new Symfony class is available since Symfony 5.4, so this change should be completely transparent to end users 🤔 In any case, I added the entry. Thanks.

[jderusse]

Do we really need an entry in the changelog? The new Symfony class is available since Symfony 5.4, so this change should be completely transparent to end users 🤔 In any case, I added the entry. Thanks.

It's required, to automate the releasing of components. I have a script that use the changelog to define the next version (patch / minor)

[jderusse]

Thank you @javiereguiluz