minor #6094 [Form] Added a missing php opening tag (dev-symfony-void)

This PR was merged into the 2.3 branch.

Discussion
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[Form] Added a missing php opening tag

Commits
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62f54a8 [Form] Added a missing php opening tag

Author: xabbuh

cookbook/form/form_customization.rst

@@ -682,7 +682,7 @@ customize the ``name`` field only:
 
         <!-- app/Resources/views/Form/_product_name_widget.html.php -->
         <div class="text_widget">
-              echo $view['form']->block('form_widget_simple') ?>
+            <?php echo $view['form']->block('form_widget_simple') ?>
         </div>
 
 Here, the ``_product_name_widget`` fragment defines the template to use for the