HTML5-PHP parser fails if `extendedUrlContext` is set

HTML5-PHP parser fails if staatic_extended_url_context is set

## Log Message:

Error: Object of class DOMElement could not be converted to string in /Users/apple/Local Sites/mysite/app/public/wp-content/plugins/staatic/vendor/staatic/crawler/src/UrlExtractor/HtmlUrlExtractor.php:187
Stack trace:
#0 /Users/apple/Local Sites/aibms/app/public/wp-content/plugins/staatic/vendor/staatic/crawler/src/UrlExtractor/HtmlUrlExtractor.php(104): Staatic\Crawler\UrlExtractor\HtmlUrlExtractor->handleElementAttributes(Object(DOMElement), Array, Object(Staatic\Vendor\GuzzleHttp\Psr7\Uri))

## Code In question

if ($this->extendedUrlContext) {
    $context['htmlElement'] = (string)$element;
 }