minor symfony#12167 Use correct code-block (OskarStark)

This PR was merged into the 4.3 branch.

Discussion
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Use correct code-block

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Commits
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1aee6d7 Use correct code-block

Author: OskarStark

routing.rst

@@ -1910,7 +1910,7 @@ Generating URLs in Templates
 The Twig template language used in :doc:`Symfony templates </templating>`
 provides some functions to generate both relative and absolute URLs:
 
-.. code-block:: twig
+.. code-block:: html+twig
 
     {# generates relative URLs #}
     <a href="{{ path('sign_up') }}">Sign up</a>