zuul: move the next lanes to OpenStack 2026.1

[ideaship]

Step 2 of:

• Roll testbed OpenStack version lanes forward (current/next are stale) #2900

Moves both next lanes to OpenStack 2026.1:

• testbed-deploy-next-in-a-nutshell-ubuntu-24.04 — openstack_version: "2025.1" → "2026.1"
• testbed-upgrade-stable-next-ubuntu-24.04 — openstack_version_next: "2025.2" → "2026.1"

The 2026.1 gaps are currently invisible to CI and would otherwise surface at the
OSISM 11 release. They are tracked in:

• Add OpenStack 2026.1 issues#1428

The registry blocker is gone

This description previously said to expect the lanes to fail because
registry.osism.tech carried no kolla/*:2026.1 service images and
container-images-kolla-push-2026.1 was failing. Neither holds any more,
verified 2026-09-09:

• 133 kolla/* repositories on registry.osism.tech carry a 2026.1 tag,
  against 137 for 2025.1. The difference is kolla's own: redis,
  redis-sentinel, ironic-inspector, letsencrypt-webserver,
  neutron-linuxbridge-agent, prometheus-ovn-exporter, mariadb-clustercheck
  and proxysql-3 are gone at 2026.1, while httpd, ironic-pxe-filter,
  prometheus-openstack-network-exporter and prometheus-valkey-exporter are
  new.
• Digests match the build registry — kolla/keystone:2026.1 is
  sha256:a1d74998e19d7… on both hosts — and replication now carries 2026.1 on
  the same few-second delay as every other series (2026-09-09, pushed 02:00:43Z,
  replicated 02:00:51Z).
• container-images-kolla-push-2026.1 has succeeded on every run since
  2026-09-04, periodic-midnight included.
• kolla/sbom:2026.1 is published too, so osism sync versions --openstack-version 2026.1 has a working path.

The kolla-ansible tooling image has been in place since:

• Add 2026.1 build container-image-kolla-ansible#942

So the lanes now have images to deploy. They may still fail, on the 2026.1 gaps
in the tracker above rather than on missing images, and finding that out is the
point of this change.

The buildset on this PR is from 2026-09-02, i.e. from before the images were
published, so it says nothing about the current state. Re-running needs the
zuul label removed and re-added — the pipeline triggers on labeled only.

Before merging

The tip commit, DNM: add next jobs to zuul label, swaps the label pipeline's
job list to the next and upgrade lanes so this change can actually be
exercised. It has to be dropped before merge.

Adjacent, not a blocker

osism/release latest/openstack-2026.1.yml still pins
ansible_core_version: '2.18.18', which the 2026.1 image does not honour:
kolla-ansible stable/2026.1 requires ansible-core>=2.19,!=2.19.0,<2.21, and
the uv pip install -r /repository/requirements.txt step later in the image
build overrides the pin — registry.osism.tech/osism/kolla-ansible:2026.1 ships
ansible-core 2.20.8. That version split between the managers is what this
tracks:

• current/next deploy lanes dark since 2026-07-25 — ansible-core 2.19 fact-cache namespacing vs. the shared fact cache issues#1420

Not included, deliberately

• ceph_version stays reef. Roll testbed OpenStack version lanes forward (current/next are stale) #2900 marks reef → squid "only if
  verified", and OSISM does not tie the Ceph release to the OpenStack major.
  Keeping reef also means a red lane points at 2026.1 rather than at an untested
  Ceph swap. Note scripts/prepare-ceph-configuration.sh hardcodes the reef
  ceph-pools.yml URL, so a squid move needs that made version-aware.
• environments/openstack/files/tempest/exclude.lst — cannot be reviewed for
  2026.1 before a lane produces a tempest run, and the with-tempest variants
  only run on label.

[osfrickler]

let's see things in the CI first before we merge this for real