build(python): fix `docs` and `docfx` builds#1076

ankiaga merged 1 commit intomaingoogleapis/python-spanner:mainfrom

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