Add rocky job to gate

It was made voting some time ago, but we missed also running it in gate.

With that RHEL platform test in place, we can keep c9s permanently
non-voting, which is better suited to match its instability.

Change-Id: I6712ac6dc64e4fe2203b2a5f6a381f6d2150ba0f

.zuul.yaml

@@ -697,8 +697,6 @@
     description: CentOS 9 Stream platform test
     nodeset: devstack-single-node-centos-9-stream
     timeout: 9000
-    # TODO(kopecmartin) n-v until the following is resolved:
-    # https://bugs.launchpad.net/neutron/+bug/1979047
     voting: false
 
 - job:
@@ -968,11 +966,9 @@
       jobs:
         - devstack
         - devstack-ipv6
-        # TODO(kopecmartin) n-v until the following is resolved:
-        # https://bugs.launchpad.net/neutron/+bug/1979047
-        # - devstack-platform-centos-9-stream
         - devstack-platform-debian-bullseye
         - devstack-platform-ubuntu-focal
+        - devstack-platform-rocky-blue-onyx
         - devstack-enforce-scope
         - devstack-multinode
         - devstack-unit-tests