Generate homepage less frequently

With the current schedule polling every 10 minutes we hit rate limits
too often, hence reduce polling interval to 20 minutes.

Issue: Issue 12944
Change-Id: If9a7b29f88a5ebf2a37ec9b1355045b447e72adc
diff --git a/jenkins/homepage.yaml b/jenkins/homepage.yaml
index a865cde..6b3f38d 100644
--- a/jenkins/homepage.yaml
+++ b/jenkins/homepage.yaml
@@ -10,5 +10,5 @@
               - master
     triggers:
       - pollscm:
-          cron: "H/10 * * * *"
+          cron: "H/20 * * * *"
       - timed: "@midnight"