zuul: Declare queue at top level

Zuul deprecated declaring shared queues at a pipeline level with
release 4.1.0[1]. This updates the job definition to use the top level
declaration instead.

See [2] for details.

[1] https://zuul-ci.org/docs/zuul/latest/releasenotes.html#relnotes-4-1-0-deprecation-notes
[2] http://lists.openstack.org/pipermail/openstack-discuss/2022-May/028603.html

Change-Id: Ib54f5944cfd803baa4044858c097fc71f1ffb789
(cherry picked from commit 4a898171f0)
(cherry picked from commit f4904ff7af)

.zuul.yaml

@@ -184,6 +184,7 @@
       - ^releasenotes/.*$
 
 - project:
+    queue: heat
     templates:
       - openstack-cover-jobs
       - openstack-python3-xena-jobs
@@ -198,7 +199,6 @@
         - heat-functional
         - heat-functional-legacy
     gate:
-      queue: heat
       jobs:
         - grenade-heat-multinode
         - heat-functional