Update tox.ini to work with 4.0

With tox release of 4.0, some parameters were deprecated and are ignored now
which causes tox failures. One of the most spread issues we have is using
`whitelist_externals` isntead of `allowlist_externals`


Change-Id: I7807b7d29f4504404253f5c42b624639c8b19c97

tox.ini

@@ -19,7 +19,7 @@ passenv =
     HTTPS_PROXY
     no_proxy
     NO_PROXY
-whitelist_externals =
+allowlist_externals =
     bash
 setenv =
     PYTHONUNBUFFERED=1
@@ -44,7 +44,7 @@ commands =
 
 [testenv:pdf-docs]
 deps = {[testenv:docs]deps}
-whitelist_externals =
+allowlist_externals =
   make
 commands =
   sphinx-build -W -b latex doc/source doc/build/pdf