Remove trailing whitespace

Author: Arkalo2

forms.rst

@@ -1002,7 +1002,7 @@ You can get the referral code via ``getExtraData``::
     $extraData = $form->getExtraData();
     $referralCode = $extraData['referralCode'] ?? null;
     
-> Don't forget to set :ref:`allow_extra_fields <allow-extra-fields>` option to ``true`` on your form 
+> Don't forget to set :ref:`allow_extra_fields <allow-extra-fields>` option to ``true`` on your form
 
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