Allow Twig\Environment::render to be tainted even when using variables as arguments.

[adrienlucas]

Before this, taints were not forwarded if the call to Twig\Environment::render was made using variables as arguments (i.e. template name and template parameters).

In other words :

$untrusted = $_GET['untrusted'];

// this was the only supported syntax before
$twig->render('index.html.twig', ['untrusted' => $untrusted]);

// this is now supported
$template = 'index.html.twig';
$parameters = ['untrusted' => $untrusted];
$twig->render($template, $parameters);