minor #12089 Update multiple_buttons.rst (Romaxx)

This PR was submitted for the 4.3 branch but it was merged into the 3.4 branch instead (closes #12089).

Discussion
----------

Update multiple_buttons.rst

Reference to symfony/symfony#32932

Commits
-------

194bca1 Update multiple_buttons.rst

Author: javiereguiluz

form/multiple_buttons.rst

@@ -35,3 +35,9 @@ Or you can get the button's name by using the
     if ($form->getClickedButton() && 'saveAndAdd' === $form->getClickedButton()->getName()) {
         // ...
     }
+    
+If you have multiple buttons with the same name, each nested in multiple subforms, use direct reference instead the name to get the right button
+
+    if ($form->getClickedButton() && $form->getClickedButton() === $form->get('saveAndAdd')){
+
+    }