Fix deprecated zuul queue syntax

Zuul deprecated (and now removed) declaring shared queues at a pipeline
level [1]. This patch fixes the syntax to make the gate work again for
solum stable branches.

[1] https://lists.openstack.org/pipermail/openstack-discuss/2022-May/028603.html

Change-Id: I7727f3d19e0b40e7faacc14677d3815839df4600

Author: osfrickler

.zuul.yaml

@@ -1,4 +1,5 @@
 - project:
+    queue: solum
     templates:
       - openstack-cover-jobs
       - openstack-python3-yoga-jobs
@@ -14,7 +15,6 @@
         - solum-tox-bandit-baseline:
             voting: false
     gate:
-      queue: solum
       jobs:
         - solum-devstack
         - solum-tempest-ipv6-only