zuul: Make openstackclient-check-plugins voting

This will ensure we do not forget to ignore a module when migrating
plugins in-tree.

Change-Id: Id4dd657746f7c5f8ebf5ef55964593123303b996
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Depends-on: https://review.opendev.org/c/openstack/openstackclient/+/970618

.zuul.yaml

@@ -173,6 +173,8 @@
       - release-notes-jobs-python3
     check:
       jobs:
+        - openstackclient-check-plugins:
+            voting: true
         - osc-build-image:
             voting: false
         - osc-functional-devstack