minor symfony#46913 Check for null instead of type (ihmels)

This PR was submitted for the 6.2 branch but it was merged into the 5.4 branch instead.

Discussion
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Check for null instead of type

| Q             | A
| ------------- | ---
| Branch?       | 6.2
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | n/a
| License       | MIT
| Doc PR        | n/a

`LogoutEvent::getResponse()` returns a `Response` or `null`, so it is not necessary to check the type, but whether the value is null.

Commits
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f545be9 Check for null instead of type

Author: wouterj

src/Symfony/Component/Security/Http/Firewall/LogoutListener.php

@@ -121,8 +121,7 @@ public function authenticate(RequestEvent $event)
         $logoutEvent = new LogoutEvent($request, $this->tokenStorage->getToken());
         $this->eventDispatcher->dispatch($logoutEvent);
 
-        $response = $logoutEvent->getResponse();
-        if (!$response instanceof Response) {
+        if (!$response = $logoutEvent->getResponse()) {
             throw new \RuntimeException('No logout listener set the Response, make sure at least the DefaultLogoutListener is registered.');
         }