Add stable/zed jobs on master gate

As zed is released, we should add its 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: I10bbcdf711ede18496545e6a4b1fd1098388e891
diff --git a/.zuul.yaml b/.zuul.yaml
index 29a7ee2..da76d7b 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -1,4 +1,10 @@
 - job:
+    name: heat-functional-zed
+    parent: heat-functional
+    nodeset: openstack-single-node-focal
+    override-checkout: stable/zed
+
+- job:
     name: heat-functional-yoga
     parent: heat-functional
     nodeset: openstack-single-node-focal
@@ -25,6 +31,7 @@
       jobs:
         - heat-functional
         - heat-functional-legacy
+        - heat-functional-zed
         - heat-functional-yoga
         - heat-functional-xena
         - heat-functional-wallaby