fix tox compatibility

Author: benzekrimaha

docs/tox.ini

@@ -21,7 +21,7 @@ deps =
 #     {[testenv]deps}
 commands =
     pip install --upgrade pip
-    pip install --upgrade setuptools
+    pip install setuptools==64.0.0
     pip install -r{toxinidir}/docsource/requirements.txt
     pip list
     make -C docsource {posargs:html}