bug(html): invisible links are reported in metadata

[scanny]

Summary
partition_html() adds an empty link_texts entry for an <a> element that has no text or whitespace-only text (and therefore is not displayed or clickable in a browser).

To Reproduce

html_text = "<p>Time is an illusion. <a href="http://seo.com"></a>Lunchtime doubly so.</p>"

elements = partition_html(text=html_text)
print(f"{elements_to_json(elements, indent=2)}")

Expected:

[
  {
    "element_id": "5fe7349cfd2346fed5d638c216d7506e",
    "metadata": {
      "filetype": "text/html",
      "languages": ["eng"]
    },
    "text": "Time is an illusion. Lunchtime doubly so.",
    "type": "NarrativeText"
  }
]

Actual:

[
  {
    "element_id": "5fe7349cfd2346fed5d638c216d7506e",
    "metadata": {
      "filetype": "text/html",
      "languages": ["eng"]
      "link_texts": [""],
      "link_urls": ["http://seo.com"]
    },
    "text": "Time is an illusion. Lunchtime doubly so.",
    "type": "NarrativeText"
  }
]

Additional context
Fixed by #3218. Recorded here to explain ingest test output changes and to inform CHANGELOG.