Support readthedocssinglehtmllocalmedia builder

[Robpol86]

https://readthedocs.org/api/v2/build/16796464.txt

/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/bin/python -m sphinx -T -E -W --keep-going -b readthedocssinglehtmllocalmedia -d _build/doctrees -D language=en . _build/localmedia
Running Sphinx v4.5.0
loading translations [en]... done
making output directory... done
building [mo]: targets for 0 po files that are out of date
building [readthedocssinglehtmllocalmedia]: all documents
updating environment: [new config] 3 added, 0 changed, 0 removed
reading sources... [ 33%] index
reading sources... [ 66%] install
reading sources... [100%] usage

looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
assembling single document... install usage done
writing... failed

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/cmd/build.py", line 276, in build_main
    app.build(args.force_all, filenames)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/application.py", line 330, in build
    self.builder.build_update()
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/builders/__init__.py", line 283, in build_update
    self.build(['__all__'], to_build)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/builders/__init__.py", line 350, in build
    self.write(docnames, list(updated_docnames), method)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/builders/singlehtml.py", line 155, in write
    self.write_doc(self.config.root_doc, doctree)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/builders/html/__init__.py", line 619, in write_doc
    self.docwriter.write(doctree, destination)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/docutils/writers/__init__.py", line 78, in write
    self.translate()
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/writers/html.py", line 59, in translate
    self.document.walkabout(visitor)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/docutils/nodes.py", line 227, in walkabout
    if child.walkabout(visitor):
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/docutils/nodes.py", line 227, in walkabout
    if child.walkabout(visitor):
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/docutils/nodes.py", line 227, in walkabout
    if child.walkabout(visitor):
  [Previous line repeated 3 more times]
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/docutils/nodes.py", line 219, in walkabout
    visitor.dispatch_visit(self)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/envs/latest/lib/python3.10/site-packages/sphinx/util/docutils.py", line 516, in dispatch_visit
    method(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/checkouts/latest/sphinx_carousel/nodes.py", line 94, in html_visit
    writer.starttag(
TypeError: docutils.writers._html_base.HTMLTranslator.starttag() argument after ** must be a mapping, not NoneType

Exception occurred:
  File "/home/docs/checkouts/readthedocs.org/user_builds/sphinx-carousel/checkouts/latest/sphinx_carousel/nodes.py", line 94, in html_visit
    writer.starttag(
TypeError: docutils.writers._html_base.HTMLTranslator.starttag() argument after ** must be a mapping, not NoneType
The full traceback has been saved in /tmp/sphinx-err-8tn5zgx_.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!