Use stable constraints for Tempest venv for stable/ussuri|victoria

we do have legacy jobs in ussuri and might be in victoria also and
as we are pinning tempest in both stable branches they need to use the
respective stable branches constraints instead of master constraints.

- https://review.opendev.org/q/topic:ussuri-pin-tempest
- https://review.opendev.org/q/topic:victoria-pin-tempest

Hoping this is last time we are updating the tempest setting in d-g
as all jobs in victoria onwards should be migrated to zuulv3 native.

Change-Id: I07e1cb9b038e8d0c8ce83e8554188f9eb72cb339

devstack-vm-gate.sh

@@ -864,7 +864,10 @@ if [[ "$DEVSTACK_GATE_TEMPEST" -eq "1" ]]; then
     # instead of using master. We need to export it via env var TOX_CONSTRAINTS_FILE
     # so that initial creation of tempest tox use stable branch constraint
     # instead of master constraint as defined in tempest/tox.ini
-    stable_for_u_c="stable/[o-t]"
+    # Hoping we do not need to update these setting anymore as victoria onwards
+    # all jobs are supposed to be migrated to zuulv3 native jobs and does not require
+    # devstack-gate.
+    stable_for_u_c="stable/[o-v]"
     if [[ "$ZUUL_BRANCH" =~ $stable_for_u_c  ]] ; then
         export TOX_CONSTRAINTS_FILE=$BASE/new/requirements/upper-constraints.txt
     else