minor #5511 [HttpKernel] Fix use statement (dunglas)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #5511).

Discussion
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[HttpKernel] Fix use statement

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | n/a

Commits
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6a9fe71 [HttpKernel] Fix use statement

Author: xabbuh

components/http_kernel/introduction.rst

@@ -691,7 +691,7 @@ can be used to figure out if the current request is a "master" or "sub" request.
 For example, a listener that only needs to act on the master request may
 look like this::
 
-    use Symfony\Component\HttpKernel\HttpKernelInterface;
+    use Symfony\Component\HttpKernel\Event\GetResponseEvent;
     // ...
 
     public function onKernelRequest(GetResponseEvent $event)