minor symfony#6829 Fix a typo in an HTTP Cache code example (aybbou)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes symfony#6829).

Discussion
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Fix a typo in an HTTP Cache code example

Commits
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69afb94 Fix a typo in an HTTP Cache code example

Author: wouterj

http_cache.rst

@@ -220,8 +220,8 @@ The *easiest* way to cache a response is by caching it for a specific amount of
         // somehow create a Response object, like by rendering a template
         $response = $this->render('blog/index.html.twig', []);
 
-        // cache for 600 seconds
-        $response->setSharedMaxAge(600);
+        // cache for 3600 seconds
+        $response->setSharedMaxAge(3600);
 
         // (optional) set a custom Cache-Control directive
         $response->headers->addCacheControlDirective('must-revalidate', true);