cyborg Fix tox4 error

Other failure is due to the skipsdist = True.

Fixing tox.ini for tox4 changes.

Change-Id: I70e5b8569efb0f898a444de4ed043ed3b7b77f78

tox.ini

@@ -1,7 +1,6 @@
 [tox]
 minversion = 3.18.0
 envlist = py3,pep8
-skipsdist = True
 # Automatic envs (pyXX) will only use the python version appropriate to that
 # env and ignore basepython inherited from [testenv] if we set
 # ignore_basepython_conflict.
@@ -91,6 +90,9 @@ ignore-path = .venv,.git,.tox,*cyborg/locale*,*lib/python*,*cyborg.egg*,api-ref/
 [testenv:docs]
 description =
   Build main documentation.
+allowlist_externals =
+  sphinx-build
+  rm
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt