build(python): fix `docs` and `docfx` builds#939

rwhogg merged 8 commits intomaingoogleapis/python-ndb:mainfrom

owl-bot-update-lock-5ea6d0ab82c956b50962f91d94e206d3921537ae5fe1549ec5326381d8905cfagoogleapis/python-ndb:owl-bot-update-lock-5ea6d0ab82c956b50962f91d94e206d3921537ae5fe1549ec5326381d8905cfaCopy head branch name to clipboard