Add stable/wallaby jobs on master gate

Stable/wallaby is released so we should add
their job on master gate to keep branchless tempest
plugins compatible to stable branch.

Ref: Tempest plugins guide for stable branch testing:
- https://docs.openstack.org/tempest/latest/stable_branch_testing_policy.html

Change-Id: I3e8534fdc91a9e94fa82ce6504f36f3d0b5aed6c
diff --git a/.zuul.yaml b/.zuul.yaml
index 59bd271..753b57b 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -6,6 +6,7 @@
       jobs:
         - barbican-tempest-plugin-simple-crypto
         - barbican-tempest-plugin-simple-crypto-secure-rbac
+        - barbican-tempest-plugin-simple-crypto-wallaby
         - barbican-tempest-plugin-simple-crypto-victoria
         - barbican-tempest-plugin-simple-crypto-ussuri
         - barbican-tempest-plugin-simple-crypto-train
@@ -77,6 +78,11 @@
               enforce_scope: True
 
 - job:
+    name: barbican-tempest-plugin-simple-crypto-wallaby
+    parent: barbican-tempest-plugin-simple-crypto
+    override-checkout: stable/wallaby
+
+- job:
     name: barbican-tempest-plugin-simple-crypto-victoria
     parent: barbican-tempest-plugin-simple-crypto
     nodeset: openstack-single-node-bionic