Disable concurrent execution for push-upstream jobs

Parallel push from nordix can triggered a race condition in
upstream gerrit that will resulted in a duplicated review
instead of a single review for the first push and the second push.

Change-Id: I613531329aa4185d3f21f1c42c8d031e6cf95b4e
diff --git a/jjb/opendev/global-templates-opendev-push-upstream.yaml b/jjb/opendev/global-templates-opendev-push-upstream.yaml
index 5b8bfb6..c0c279e 100644
--- a/jjb/opendev/global-templates-opendev-push-upstream.yaml
+++ b/jjb/opendev/global-templates-opendev-push-upstream.yaml
@@ -5,7 +5,7 @@
 
     disabled: false
 
-    concurrent: true
+    concurrent: false
 
     properties:
       - logrotate