Build its-storyboard on stable-2.16

Change-Id: I36fb9e31281f8cd019955dcf9f4f415fdcefa4d1
diff --git a/jenkins/gerrit-bazel-plugin-its-storyboard.yaml b/jenkins/gerrit-bazel-plugin-its-storyboard.yaml
index bb05a89..32d4190 100644
--- a/jenkins/gerrit-bazel-plugin-its-storyboard.yaml
+++ b/jenkins/gerrit-bazel-plugin-its-storyboard.yaml
@@ -4,3 +4,4 @@
       - 'plugin-its-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-2.16