minor #16443 Update extension.rst (issamkhadiri1989)

This PR was submitted for the 6.0 branch but it was merged into the 4.4 branch instead.

Discussion
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Update extension.rst

when using  `DependencyInjection\Extension\Extension`, the `addAnnotatedClassesToCompile` is not available. so it should be mentionned that we need to use `HttpKernel\DependencyInjection\Extension` instead when the method `addAnnotatedClassesToCompile`  must be used

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Commits
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7e3106b Update extension.rst

Author: wouterj

bundles/extension.rst

@@ -34,7 +34,7 @@ This is how the extension of an AcmeHelloBundle should look like::
     namespace Acme\HelloBundle\DependencyInjection;
 
     use Symfony\Component\DependencyInjection\ContainerBuilder;
-    use Symfony\Component\DependencyInjection\Extension\Extension;
+    use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 
     class AcmeHelloExtension extends Extension
     {