Move stable branch gate job to stable/victoria

We have stable/victoria branch as latest stable and
d-g test only latest stable branch to make sure the compatibility
of legacy jobs.

This commit moves the legacy stable job testing to stable/victoria.

Change-Id: I78a0f55c360df2804200cc801109741276248550

playbooks/legacy/tempest-neutron-full/run.yaml

@@ -52,7 +52,7 @@
           # be enough to make sure devstack-gate keep working for
           # stable branch legacy jobs which are not yet migrated
           # to Zuul v3 native jobs.
-          export BRANCH_OVERRIDE=stable/ussuri
+          export BRANCH_OVERRIDE=stable/victoria
           if [ "$BRANCH_OVERRIDE" != "default" ] ; then
               export OVERRIDE_ZUUL_BRANCH=$BRANCH_OVERRIDE
           fi