We pinned tox<4 in ensure-tox pre.yaml playbook
- https://review.opendev.org/q/I9a138af94dedc0d8ce5a0d519d75779415d3c30b
but did not realize that it is used in run-both.yaml playbook
also where we should pin too.
Depends-On: https://review.opendev.org/c/openstack/swift/+/869520
Change-Id: I4407f7036e3fd51ac79f68791151c3f9cd03bd01
(cherry picked from commit 689b399e3a)