Description
See https://readthedocs.org/projects/mypy/builds/
It looks like this is related to sphinx-doc/sphinx#9777 , in which case the quickest resolution is probably just pinning some package versions.
However, it looks like the ReadTheDocs build its own instructions that are unrelated to tox -e docs
/ the versions specified in the mypy repo. I'm not really familiar with RTD — where are its build steps coming from and who has permission to change it?