Reduce polling time to 5m

Now that the branch scanning takes around 10s
we can make the polling for new changes to build
more frequent, so that the maximum lead time to start
a verification is reduced to 5m.

Change-Id: I382f949d4faa651b246b9eb5387e690c17dc0c3d
diff --git a/jenkins/gerrit-verifier.yaml b/jenkins/gerrit-verifier.yaml
index 519df45..cee50c1 100644
--- a/jenkins/gerrit-verifier.yaml
+++ b/jenkins/gerrit-verifier.yaml
@@ -156,4 +156,4 @@
             all-branches:
               - suppress-scm-triggering: false
               - pipeline-branch-durability-override: max-survivability
-    periodic-folder-trigger: 10m
+    periodic-folder-trigger: 5m