title: Can't add "markdown_to_html" filter to twig
body: <p>I want to use the <code>markdown_to_html</code> filter to render makrdown inside my template, so I tried following the <a href="https://twig.symfony.com/doc/3.x/filters/markdown_to_html.html" rel="nofollow noreferrer">instructions</a> in the docs but the filter is not added correctly. The error I get when rendering the template is <em>Message: Unknown "markdown_to_html" filter.</em></p>
  
  <p>Here's my code:</p>
  
  <pre><code>// Load twig and the markdown extension
  
  require_once "../vendor/autoload.php";
  $loader = new \Twig\Loader\FilesystemLoader("../templates");
  $twig = new \Twig\Environment($loader, [
    "cache" =&gt; "../cache/twig",
    "debug" =&gt; true,
    "autoescape" =&gt; false,
  ]);
  
  use Twig\Extra\Markdown\DefaultMarkdown;
  use Twig\Extra\Markdown\MarkdownRuntime;
  use Twig\RuntimeLoader\RuntimeLoaderInterface;
  
  $twig-&gt;addRuntimeLoader(new class implements RuntimeLoaderInterface {
    public function load($class) {
      if (MarkdownRuntime::class === $class) {
        return new MarkdownRuntime(new DefaultMarkdown());
      }
    }
  });
  
  // Read md file and render template
  
  $markdown = file_get_contents("content/text.md");
  try {
    echo $twig-&gt;render("template.phtml", ["text" =&gt; $markdown]);
  }
  catch(Exception $e) {
    echo 'Message: ' . $e-&gt;getMessage();
  }
  
  
  </code></pre>
  
  <p>The template:</p>
  
  <pre><code>  {% apply markdown_to_html %}
      {{ text }}
    {% endapply %}
  </code></pre>
  
  <p>I added <code>twig/twig</code> and <code>twig/markdown-extra</code>, both are version <code>3.0</code>. Thanks for any help.</p>