Limit tox version to <4

This patch is a workaround until we find why fullstack job is failing
with tox 4.

Depends-On: https://review.opendev.org/c/zuul/zuul-jobs/+/866943

Related-Bug: #1999558
Change-Id: I9c62d429bb819336da05055fecd08e3816986bf8

playbooks/configure_functional_job.yaml

@@ -1,6 +1,8 @@
 - hosts: all
   roles:
-    - ensure-tox
+    - role: ensure-tox
+      vars:
+        ensure_tox_version: "<4"
     # TODO(slaweq): remove it when nftables will support syntax for src and
     # destination IP addresses in arp tables:
     - legacy_ebtables

playbooks/run_functional_job.yaml

@@ -4,5 +4,7 @@
       bindep_profile: test
       bindep_dir: "{{ zuul_work_dir }}"
     - test-setup
-    - ensure-tox
+    - role: ensure-tox
+      vars:
+        ensure_tox_version: "<4"
     - tox

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 envlist = docs,py38,pep8
 minversion = 3.18.0
-skipsdist = True
+skipsdist = False
 ignore_basepython_conflict = True
 
 [testenv]