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: I55cade793fc74fd5555c0f520bc132916343330e

tox.ini

@@ -21,7 +21,7 @@ passenv =
     TESTING_BRANCH
     TESTING_HOME
     USER
-whitelist_externals =
+allowlist_externals =
     bash
 setenv =
     PYTHONUNBUFFERED=1
@@ -41,7 +41,7 @@ commands =
 
 [testenv:pdf-docs]
 deps = {[testenv:docs]deps}
-whitelist_externals =
+allowlist_externals =
   make
 commands =
   sphinx-build -W --keep-going -b latex doc/source doc/build/pdf