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: I04352e372c8ea2008f7ab0e7cdfa1d8b975e4251

tox.ini

@@ -12,11 +12,11 @@ setenv = VIRTUAL_ENV={envdir}
          OS_STDERR_CAPTURE=1
          OS_TEST_TIMEOUT=60
 deps = -r{toxinidir}/test-requirements.txt
-whitelist_externals = reno
+allowlist_externals = reno
 
 [testenv:linters]
 basepython = python3
-whitelist_externals = bash
+allowlist_externals = bash
 commands =
   bash -c "find {toxinidir}          \
          -not \( -type d -name .?\* -prune \) \
@@ -119,7 +119,7 @@ deps = -r{toxinidir}/doc/requirements.txt
 commands =
     rm -rf doc/build
     sphinx-build -a -E -W -d doc/build/doctrees -b html doc/source doc/build/html
-whitelist_externals = rm
+allowlist_externals = rm
 
 [testenv:releasenotes]
 basepython = python3
@@ -127,7 +127,7 @@ deps = -r{toxinidir}/doc/requirements.txt
 commands =
     rm -rf releasenotes/build
     sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
-whitelist_externals = rm
+allowlist_externals = rm
 
 [testenv:newnote]
 basepython = python3
@@ -145,7 +145,7 @@ deps =
 commands =
   rm -rf api-ref/build
   sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html
-whitelist_externals = rm
+allowlist_externals = rm
 
 [bandit]
 # B411: blacklist Using xmlrpclib