CI: set previous_release to Victoria

This controls which release we are upgrading from.

Change-Id: I7abb6a25becde1e8855d1d177fafcb618789f0a1

zuul.d/jobs.yaml

@@ -76,7 +76,7 @@
       - ^tox.ini$
     vars:
       # Name of the release to upgrade from for upgrade jobs.
-      previous_release: ussuri
+      previous_release: victoria
       logs_dir: "/tmp/logs"
       kayobe_src_dir: "{{ ansible_env.PWD ~ '/' ~ zuul.projects['opendev.org/openstack/kayobe'].src_dir }}"
       kayobe_config_src_dir: "{{ ansible_env.PWD ~ '/' ~ zuul.projects['opendev.org/openstack/kayobe-config-dev'].src_dir }}"