Comment 2 for bug 1988092

Reviewed: https://review.opendev.org/c/openstack/charm-keystone-saml-mellon/+/870348
Committed: https://opendev.org/openstack/charm-keystone-saml-mellon/commit/832b46a29b59102b1defb962ae31ba6e380042d2
Submitter: "Zuul (22348)"
Branch: stable/ussuri

commit 832b46a29b59102b1defb962ae31ba6e380042d2
Author: Corey Bryant <email address hidden>
Date: Fri Jan 13 15:06:10 2023 -0500

    Pin tox to < 4.0.0

    Tox 4.0.0 was recently released and it has several breaking changes.
    We pin to < 4.0.0 here. We are planning to move forward only on the
    master charm branches.

    Tox is also pinned to < 4.0.0 for stable branches in upstream
    openstack-zuul-jobs as well as in zosci-config. However, the
    requires= section in the charm's tox.ini file ends up installing
    tox>4, wiping out the zuul-pinned tox<4 that was already installed
    installed. This patch fixes that.

    Added libxml2-dev to the list of dependencies in src/layer.yaml, this
    explicit dependency is needed only when deploying on Bionic.

    Related-Bug: #2002788
    Closes-Bug: #1988092
    Change-Id: I4a5a4f3cafebb986c64e54d2a3a0bd048adf0933