Update tox.ini to work with tox 4

This change will allow this repo to pass zuul now
that this has merged:
https://review.opendev.org/c/zuul/zuul-jobs/+/866943

Tox 4 deprecated whitelist_externals.
Replace whitelist_externals with allowlist_externals

Partial-Bug: #2000399

Signed-off-by: Al Bailey <al.bailey@windriver.com>
Change-Id: I03c6cd50b9545b8553e7b1175a3684901beb3f52

tox.ini

@@ -17,14 +17,14 @@ deps = bindep
 commands = bindep test
 
 [testenv:docs]
-whitelist_externals = bash
+allowlist_externals = bash
 commands =
   bash -c 'if [ -d doc ]; then \
     python setup.py build_sphinx; \
   fi'
 
 [testenv:linters]
-whitelist_externals = bash
+allowlist_externals = bash
 passenv =
   # NOTE(pabelanger): if you'd like to run tox -elinters locally, you'll need
   # to export ANSIBLE_ROLES_PATH pointing to the currect repos.
@@ -96,7 +96,7 @@ install_command = pip install -U \
     -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/stable/stein/upper-constraints.txt} \
     {opts} {packages}
 deps = -r{toxinidir}/test-requirements.txt
-whitelist_externals = bash
+allowlist_externals = bash
 commands =
   bash -c 'if [ -d {toxinidir}/../zuul-jobs ]; then jobsdir={toxinidir}/../zuul-jobs; \
          else jobsdir={toxinidir}/../stx-zuul-jobs; \