minor #17441 Replace annotation by attribute (ffouillet)

This PR was submitted for the 6.1 branch but it was merged into the 6.0 branch instead.

Discussion
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Replace annotation by attribute

Replace Annotation in custom constraint declaration by #[\Attribute] which is more up to date

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Commits
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620e6b4 Update custom_constraint.rst

Author: xabbuh

validation/custom_constraint.rst

@@ -214,9 +214,7 @@ email. First, create a constraint and override the ``getTargets()`` method::
 
     use Symfony\Component\Validator\Constraint;
 
-    /**
-     * @Annotation
-     */
+    #[\Attribute]
     class ConfirmedPaymentReceipt extends Constraint
     {
         public string $userDoesNotMatchMessage = 'User\'s e-mail address does not match that of the receipt';