Upin the versions of tox

Unpin the versions of tox, setuptools, etc. This removes the issue
with tox 4.x breaking the virtualenv dependencies.

Change-Id: I103e16c70aee394331b37ec0cf323e014011d3ae

pip.sh

@@ -1,18 +0,0 @@
-#!/usr/bin/env bash
-#
-# This file is managed centrally by release-tools and should not be modified
-# within individual charm repos.  See the 'global' dir contents for available
-# choices of tox.ini for OpenStack Charms:
-#     https://github.com/openstack-charmers/release-tools
-#
-# setuptools 58.0 dropped the support for use_2to3=true which is needed to
-# install blessings (an indirect dependency of charm-tools).
-#
-# More details on the beahvior of tox and virtualenv creation can be found at
-# https://github.com/tox-dev/tox/issues/448
-#
-# This script is wrapper to force the use of the pinned versions early in the
-# process when the virtualenv was created and upgraded before installing the
-# depedencies declared in the target.
-pip install 'pip<20.3' 'setuptools<50.0.0'
-pip "$@"

tox.ini

@@ -14,33 +14,25 @@ skipsdist = True
 sitepackages = False
 # NOTE: Avoid false positives by not skipping missing interpreters.
 skip_missing_interpreters = False
-# NOTES:
-# * We avoid the new dependency resolver by pinning pip < 20.3, see
-#   https://github.com/pypa/pip/issues/9187
-# * Pinning dependencies requires tox >= 3.2.0, see
-#   https://tox.readthedocs.io/en/latest/config.html#conf-requires
-# * It is also necessary to pin virtualenv as a newer virtualenv would still
-#   lead to fetching the latest pip in the func* tox targets, see
-#   https://stackoverflow.com/a/38133283
-requires =
-  pip < 20.3
-  virtualenv < 20.0
-  setuptools < 50.0.0
 
 # NOTE: https://wiki.canonical.com/engineering/OpenStack/InstallLatestToxOnOsci
 minversion = 3.18.0
 
 [testenv]
-setenv = VIRTUAL_ENV={envdir}
-         PYTHONHASHSEED=0
-         CHARM_DIR={envdir}
-install_command =
-  {toxinidir}/pip.sh install {opts} {packages}
+setenv =
+  VIRTUAL_ENV={envdir}
+  PYTHONHASHSEED=0
+  CHARM_DIR={envdir}
 commands = stestr run --slowest {posargs}
 allowlist_externals =
-    charmcraft
-    rename.sh
-passenv = HOME TERM CS_* OS_* TEST_*
+  charmcraft
+  rename.sh
+passenv =
+  HOME
+  TERM
+  CS_*
+  OS_*
+  TEST_*
 deps = -r{toxinidir}/test-requirements.txt
 
 [testenv:build]