GHSA-Q76J-GCG9-VXC6 Hugo: XSS via unescaped code-fence language in default code block renderer

Hugo's default code-block renderer wrote the Markdown code-fence language / info-string into the wrapper without HTML escaping. A fence info-string containing a quote and a payload breaks out of the attribute and injects a live script element. This is not an issue if you fully trust every file...