fix: treat spinx warnings as errors

Author: majorgreys

tox.ini

@@ -510,7 +510,7 @@ basepython=python3.7
 
 [testenv:docs]
 deps = sphinx
-commands = sphinx-build -b html docs docs/_build/html
+commands = sphinx-build -W -b html docs docs/_build/html
 basepython = python
 
 # do not use develop mode with celery as running multiple python versions within