minor #18407 [Security] Update voters.rst (baptistepottier)

This PR was submitted for the 6.4 branch but it was merged into the 6.2 branch instead.

Discussion
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[Security] Update voters.rst

use constant of class and not string (in twig too)

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Commits
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1799a49 Update voters.rst

Author: javiereguiluz

security/voters.rst

@@ -105,7 +105,7 @@ code like this:
             public function show(Post $post): Response
             {
                 // check for "view" access: calls all voters
-                $this->denyAccessUnlessGranted('view', $post);
+                $this->denyAccessUnlessGranted('PostVoter::VIEW', $post);
 
                 // ...
             }
@@ -114,7 +114,7 @@ code like this:
             public function edit(Post $post): Response
             {
                 // check for "edit" access: calls all voters
-                $this->denyAccessUnlessGranted('edit', $post);
+                $this->denyAccessUnlessGranted(PostVoter::EDIT, $post);
 
                 // ...
             }