[dev][infra][tact-sig] Updating Zuul's default-ansible-version to 6

Just a heads up for folks not following the OpenDev Collaboratory's service-announce mailing list... now that Zed is officially released, we'll be increasing the default Ansible version for Zuul jobs from 5 to 6 in preparation for Zuul to drop Ansible 5 support in coming weeks. See the full announcement here:

https://lists.opendev.org/pipermail/service-announce/2022-October/000046.htm...