Update tox.ini for tox v4

This convers whitelist_externals to allowlist_externals to make tox v4
happy. Note that this may not be a complete fix for tox v4 as
project-config isn't tested speculatively which makes it harder to find
all the cases.

Change-Id: Ia44a2ef83cdc57d0bb74c72ea5c95078b53ccaec

tox.ini

@@ -8,7 +8,11 @@ passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 basepython = python3
 
 [testenv:linters]
-whitelist_externals = bash
+allowlist_externals =
+  bash
+  {toxinidir}/tools/ansible-lint-roles-cache.sh
+  {toxinidir}/tools/run-bashate.sh
+  {toxinidir}/tools/zuul-projects-checks.py
 setenv =
   # NOTE(ianw) : In the gate job openstack-zuul-jobs-linters this is
   # overridden to the Zuul checkouts of the projects.  Locally,
@@ -110,7 +114,7 @@ commands =
   {toxinidir}/tools/nodepool-validate.sh
 
 [testenv:add-projects-to-main]
-whitelist_externals =
+allowlist_externals =
   git
 deps =
   ruamel.yaml