Sphinx 3.4 (test?) compatibility

[speedyleion]

It looks like sphinx 3.4 made changes that cause test failures

It looks like only one set of unit tests fail, so it may be that the sphinx test environment changed.
Rolling back to sphinx 3.3 works.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c:\git\sphinx-c-autodoc\.tox\py37\lib\site-packages\sphinx_c_autodoc\__init__.py:422: in __init__
    super().__init__(directive, name, indent)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <sphinx_c_autodoc.CTypeDocumenter object at 0x000001CE7FAAEF08>
directive = <sphinx.ext.autodoc.directive.DocumenterBridge object at 0x000001CE7FAAECC8>, name = 'my_name', indent = ''

    def __init__(self, directive: "DocumenterBridge", name: str, indent: str = '') -> None:
        self.directive = directive
>       self.config = directive.env.config
E       AttributeError: 'NoneType' object has no attribute 'config'

c:\git\sphinx-c-autodoc\.tox\py37\lib\site-packages\sphinx\ext\autodoc\__init__.py:330: AttributeError