Remove usage of deprecated Extension class

Author: emodric

bundle/DependencyInjection/NetgenSiteExtension.php

@@ -12,10 +12,10 @@
 use Symfony\Component\Config\Loader\LoaderResolver;
 use Symfony\Component\Config\Resource\FileResource;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Extension\Extension;
 use Symfony\Component\DependencyInjection\Extension\PrependExtensionInterface;
 use Symfony\Component\DependencyInjection\Loader\GlobFileLoader;
 use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;
-use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 use Symfony\Component\Yaml\Yaml;
 
 use function count;