Add rel="noopener"

It's a good practice to make target="_blank" links to cross-origin destination not give any control over original window to the site that's opened if it's not needed. And it's not needed here.
Also, lighthouse complains about it, so this small change will improve the "Best Practices" score there :)

templates/partials/cookie-consent.tpl

@@ -1,4 +1,4 @@
 <div class="cookie-consent">
     <button class="pull-right btn btn-primary">{dismiss}</button>
-    {message} <a target="_blank" href="{link_url}">{link}</a>
-</div>
+    {message} <a target="_blank" rel="noopener" href="{link_url}">{link}</a>
+</div>