Update reference/constraints/Callback.rst

Co-authored-by: Alexander M. Turek <me@derrabus.de>

Author: wkania

reference/constraints/Callback.rst

@@ -200,9 +200,10 @@ You can then use the following configuration to invoke this validator:
         // src/Entity/Author.php
         namespace App\Entity;
 
+        use Acme\Validator;
         use Symfony\Component\Validator\Constraints as Assert;
 
-        #[Assert\Callback(["Acme\Validator", "validate"])]
+        #[Assert\Callback([Validator::class, 'validate'])]
         class Author
         {
         }