openstack: optional installer capi-manifest test

The interface for enabling CAPI is not stable and this test may break.
Don't make it voting.

ci-operator/config/openshift/installer/openshift-installer-master__altinfra.yaml

@@ -461,6 +461,7 @@ tests:
   timeout: 6h0m0s
 - always_run: false
   as: openstack-capi-manifests
+  optional: true
   run_if_changed: openstack
   steps:
     cluster_profile: openstack-vexxhost

ci-operator/jobs/openshift/installer/openshift-installer-master-presubmits.yaml

@@ -2801,6 +2801,7 @@ presubmits:
       ci.openshift.io/generator: prowgen
       pj-rehearse.openshift.io/can-be-rehearsed: "true"
     name: pull-ci-openshift-installer-master-altinfra-openstack-capi-manifests
+    optional: true
     rerun_command: /test altinfra-openstack-capi-manifests
     run_if_changed: openstack
     spec: