Update tox.ini to work with tox 4

This change partially brings the following commit from `master`:

  commit e9bae3f7ee
  Author: Scott Little <scott.little@windriver.com>
  Date:   Mon Feb 6 13:13:41 2023 -0500
    Add git for storage of public keys and certs
  Signed-off-by: Scott Little <scott.little@windriver.com>

So that this repo is able to pass Zuul's tests and remain maintainable.

Change-Id: I07f75d20721445289d1360b9ab16518634b8c0b8
Signed-off-by: Luan Nunes Utimura <LuanNunes.Utimura@windriver.com>
(cherry picked from commit e9bae3f7ee)

tox.ini

@@ -13,7 +13,9 @@ deps = -r{toxinidir}/test-requirements.txt
 
 [testenv:linters]
 basepython = python3
-whitelist_externals = bash
+allowlist_externals = bash
+                      find
+                      xargs
 commands =
   bash -c "find {toxinidir} \
             \( -name .tox -prune \) \
@@ -32,4 +34,4 @@ basepython = python3
 # Use same environment directory as venv to save space and install time
 envdir = {toxworkdir}/venv
 commands = true
-whitelist_externals = true
+allowlist_externals = true