git: Set concurrency policy.

Change-Id: Iff4d53f7866f3069899813a4dd88703e67c0b75a
diff --git a/git/git.yaml b/git/git.yaml
index 148b21b..2e66b9d 100644
--- a/git/git.yaml
+++ b/git/git.yaml
@@ -217,6 +217,7 @@
 
 spec:
   schedule: "*/120 * * * *"
+  concurrencyPolicy: Forbid
 
   jobTemplate: