[2.2][TwigBridge] Fix form_enctype bug

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

After a copy/past error in #8675, `{{ form_enctype() }}` was not working because it results in a `Class "Symfony\Bridge\Twig\Node\FormEnctypeNode" not found` error.

This should only be merged in 2.2, as of 2.3 this is moved to the `Symfony\Bridge\Twig\Node\FormEnctypeNode` class