Build serviceuser plugin on stable-3.3

Change-Id: I5f7507412aada020d2fd700fc90558072919f1f2
diff --git a/jenkins/gerrit-bazel-plugin-serviceuser.yaml b/jenkins/gerrit-bazel-plugin-serviceuser.yaml
index 6d5d92f..31da1d8 100644
--- a/jenkins/gerrit-bazel-plugin-serviceuser.yaml
+++ b/jenkins/gerrit-bazel-plugin-serviceuser.yaml
@@ -4,6 +4,7 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.3
             - stable-3.2
             - stable-3.1
             - stable-2.16