minor #1746 [Site] Update RegistrationForm.html.twig use form_end instead of html form (daifma)

This PR was merged into the 2.x branch.

Discussion
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[Site] Update RegistrationForm.html.twig use form_end instead of html form

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Issues        | n/a
| License       | MIT

- Use `{{ form_end(form) }}` instead of `</form>`

Commits
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2d1b7ef Update RegistrationForm.html.twig

Author: kbond

ux.symfony.com/templates/components/RegistrationForm.html.twig

@@ -21,6 +21,6 @@
             >Register</button>
 
             {{ form_rest(form) }}
-        </form>
+        {{ form_end(form) }}
     {% endif %}
 </div>