Stop building Ubuntu Focal images for master

Master branch is not compatible with Ubuntu Focal.

Some projects like Octavia recently bumped
the minimal required python version to 3.9 while
the default python3 version in Focal is 3.8.

Also Nova requires Libvirt/Qemu newer than the
default versions on Ubuntu Focal.

See for example:
https://review.opendev.org/c/openstack/octavia/+/915970
https://review.opendev.org/c/openstack/nova/+/887255

Change-Id: Ida62539a250554e776eaae3fdf283716b98f8298

playbooks/vars.yaml

@@ -16,7 +16,7 @@ loci_src_dir: "src/opendev.org/openstack/loci"
 distros:
   - name: ubuntu_focal
     image: ubuntu:focal
-    release: master
+    release: "2023.1"
     buildargs:
       base:
         UBUNTU_URL: http://{{ zuul_site_mirror_fqdn }}/ubuntu/
@@ -28,11 +28,13 @@ distros:
       project:
         PROJECT: "{{ project }}"
         PROJECT_REPO: http://172.17.0.1/git/openstack/{{ project }}
-        WHEELS: 172.17.0.1:5000/loci/requirements:master-ubuntu_focal
+        PROJECT_REF: "stable/2023.1"
+        WHEELS: 172.17.0.1:5000/loci/requirements:2023.1-ubuntu_focal
         FROM: base:ubuntu_focal
       requirements:
         PROJECT: requirements
         PROJECT_REPO: http://172.17.0.1/git/openstack/requirements
+        PROJECT_REF: "stable/2023.1"
         FROM: base:ubuntu_focal
   - name: ubuntu_jammy
     image: ubuntu:jammy