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: I31e9f1b78c5a091317b8f595253f7bf6b2eccf14

tox.ini

@@ -16,7 +16,7 @@ deps = -r{toxinidir}/test-requirements.txt
 
 [testenv:linters]
 basepython = python3
-whitelist_externals = bash
+allowlist_externals = bash
 commands =
   bash -c "find {toxinidir}          \
          -not \( -type d -name .?\* -prune \) \
@@ -52,7 +52,7 @@ 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
@@ -60,7 +60,7 @@ 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 =
+allowlist_externals =
     rm
     reno