Seeing what I think is a spurious failure in make html failure on #6661, #7214, and #7215; see #7214 (comment):

Seeing this error running make html in the Documentation GHA in #6661 and now here:

Exception occurred:
  File "/opt/hostedtoolcache/Python/3.7.9/x64/lib/python3.7/site-packages/sphinx/builders/html/__init__.py", line 1039, in <lambda>
    ctx['css_files'].sort(key=lambda js: js.priority)
AttributeError: 'str' object has no attribute 'priority'
The full traceback has been saved in /tmp/sphinx-err-z6ie2z11.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!
make: *** [html] Error 2
Makefile:46: recipe for target 'html' failed

I don't see how it's related to my changes, but I'm also not seeing evidence of it in other builds or on the internet. I'll push an even more innocuous PR momentarily to get more data; maybe some unpinned pip dependency underneath sphinx has changed and broken things?

Link to Documentation GHA history: https://github.com/dask/dask/actions?query=workflow%3ADocumentation

I'll keep looking for whether something in my changes could be legitimately causing the failure in all 3 PRs, or otherwise trying to triage.