Get ready for tox 4

This patch makes tox 4 the default so that we can hopefully catch
problems locally before they block the gate.

tox changes:
- removed skipsdist=True, which in tox 4 appears to break the
  pep8 testenv (which runs check-uuid)
- made 4.0.0 the tox minversion

zuul changes:
- make the tgt job non-voting (it's failing on jammy, and we may
  be removing tgt support anyway)

Change-Id: Ic5ebb60b96d795ac0f14882772d26e6d4adca37b

.zuul.yaml

@@ -8,7 +8,11 @@
         - cinder-tempest-plugin-lvm-lio-barbican
         - cinder-tempest-plugin-lvm-lio-barbican-centos-9-stream:
             voting: false
-        - cinder-tempest-plugin-lvm-tgt-barbican
+        # FIXME: the tgt job is broken on jammy, and we may be removing tgt
+        # support anyway.  So make it non-voting until we figure out what to
+        # do about this, which should be at the March 2023 virtual PTG.
+        - cinder-tempest-plugin-lvm-tgt-barbican:
+            voting: false
         - nova-ceph-multistore:
             voting: false
         - cinder-tempest-plugin-cbak-ceph
@@ -27,7 +31,8 @@
     gate:
       jobs:
         - cinder-tempest-plugin-lvm-lio-barbican
-        - cinder-tempest-plugin-lvm-tgt-barbican
+        # FIXME: no sense running a non-voting gate job.  See comment above.
+        # - cinder-tempest-plugin-lvm-tgt-barbican
         - cinder-tempest-plugin-cbak-ceph
     experimental:
       jobs:

tox.ini

@@ -1,7 +1,9 @@
 [tox]
-minversion = 3.18.0
+minversion = 4.0.0
+# specify virtualenv here to keep local runs consistent with the
+# gate (it sets the versions of pip, setuptools, and wheel)
+requires = virtualenv>=20.17.1
 envlist = pep8
-skipsdist = True
 # this allows tox to infer the base python from the environment name
 # and override any basepython configured in this file
 ignore_basepython_conflict=true