Can't generate kolla-build.conf config sample on CentOS Stream 9

[Gaël THEROND]

As discussed over IRC, it seems kolla is having an issue generating the kolla-build.conf configuration sample.

When using a CentOS Stream 9 based distribution to build kolla-build.conf, we end up with a warning and a parsing error as of: https://paste.opendev.org/show/b6DvAUVpxaQnkQ1WR3sX/

How to reproduce:

* git clone kolla.
* checkout to 14.12.0/15.6.0 tags or even master.
* docker run --name kolla-build --rm -v "/home/fl1nt/kolla:/opt/kolla/:rw" --entrypoint /bin/bash quay.io/centos/centos:stream9 -c "dnf install -y python3-pip && pip3 install -U pip && pip3 install 'tox<4' && cd /opt/kolla/ && tox -e genconfig"

Additional informations:
We're bounding tox to versions bellow 4.x release as using 4.x release do cause another issue already reported:https://bugs.launchpad.net/kolla/+bug/2058385