Granted, it's not HTML, but you can append Markdown output directly to $GITHUB_STEP_SUMMARY without dealing with artifact uploads etc.
Similar too if the reporting captures video/screenshots of a given bug - the original report UI is far easier to deal with. Many test frameworks already natively put out an HTML report UI etc, it's just harder to get to than it should be with GH actions today.
Not sure how GHA treats it, but markdown is a subset of HTML so by default all HTML pages are valid Markdown documents. No conversion required.