Disable outdated validate_openstack pipeline

PROD-34344

Change-Id: If362fca85f4263517bcbb7f4787799085f6bb8a8
diff --git a/jenkins/client/job/validate.yml b/jenkins/client/job/validate.yml
index a59fe91..5d1dbdb 100644
--- a/jenkins/client/job/validate.yml
+++ b/jenkins/client/job/validate.yml
@@ -20,7 +20,7 @@
               keep_num: 50
             artifact:
               keep_num: 50
-          concurrent: true
+          concurrent: false
           scm:
             type: git
             url: "${_param:jenkins_gerrit_url}/mk/mk-pipelines"