Enable scenario 003 integration job

Now we use ml2+ovn in scenario 003 as the replacement of unmaintained
ml2+linuxbridge.

Depends-on: https://review.opendev.org/849080
Change-Id: Ibd494d3e8c8fc362143e93c95e72a03bde83890c

Author: kajinamit

.zuul.yaml

@@ -2,6 +2,7 @@
     templates:
       - puppet-openstack-check-jobs
       - puppet-openstack-module-unit-jobs
+      - puppet-openstack-integration-jobs-scenario003
       - puppet-openstack-integration-jobs-scenario005
       - puppet-openstack-litmus-jobs
       - release-notes-jobs-python3