minor #30633 Response prepare method update for more coherence (Damie…

…nVauchel)

This PR was merged into the 3.4 branch.

Discussion
----------

Response prepare method update for more coherence

$headers has been defined to avoid using $this->headers and is used everywhere but not in these lines.

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Commits
-------

e89c921 Response prepare method update

src/Symfony/Component/HttpFoundation/Response.php

@@ -310,9 +310,9 @@ public function prepare(Request $request)
         }
 
         // Check if we need to send extra expire info headers
-        if ('1.0' == $this->getProtocolVersion() && false !== strpos($this->headers->get('Cache-Control'), 'no-cache')) {
-            $this->headers->set('pragma', 'no-cache');
-            $this->headers->set('expires', -1);
+        if ('1.0' == $this->getProtocolVersion() && false !== strpos($headers->get('Cache-Control'), 'no-cache')) {
+            $headers->set('pragma', 'no-cache');
+            $headers->set('expires', -1);
         }
 
         $this->ensureIEOverSSLCompatibility($request);