Make centos-9-stream job voting

bug#1960346 is fixed by the below series
- https://review.opendev.org/q/(topic:bug/1960346+OR+topic:wait_until_sshable_pingable)+status:merged
and now centos-9-stream job is passing and made voting
on tempest gate.

This commit makes devstack centos9 steam platform job
as voting and add it gate pipeline too.

Change-Id: Ic35420c5d58926ae90a136045a1558112accc533

.zuul.yaml

@@ -678,7 +678,6 @@
     parent: tempest-full-py3
     description: CentOS 9 Stream platform test
     nodeset: devstack-single-node-centos-9-stream
-    voting: false
     timeout: 9000
     vars:
       configure_swap_size: 4096
@@ -894,6 +893,7 @@
       jobs:
         - devstack
         - devstack-ipv6
+        - devstack-platform-centos-9-stream
         - devstack-enforce-scope
         - devstack-multinode
         - devstack-unit-tests