minor #10854 Add $user variable in ->createForm(...) (bestog)

This PR was submitted for the 4.2 branch but it was merged into the 4.1 branch instead (closes #10854).

Discussion
----------

Add $user variable in ->createForm(...)

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/roadmap for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `master` for features of unreleased versions).

-->

Commits
-------

79aae2b Add $user variable in ->createForm(...)

Author: javiereguiluz

doctrine/registration_form.rst

@@ -152,7 +152,7 @@ saves the user::
         public function register(Request $request, UserPasswordEncoderInterface $passwordEncoder): Response
         {
             $user = new User();
-            $form = $this->createForm(RegistrationFormType::class);
+            $form = $this->createForm(RegistrationFormType::class, $user);
             $form->handleRequest($request);
 
             if ($form->isSubmitted() && $form->isValid()) {