Build serviceuser-plugin in-tree with Gerrit stable-3.0

Change-Id: Id5d3b80d8801ee2fa825a8b757d3708bac206830
diff --git a/jenkins/gerrit-buck-bazel-plugin-serviceuser.yaml b/jenkins/gerrit-buck-bazel-plugin-serviceuser.yaml
index 4575146..3398232 100644
--- a/jenkins/gerrit-buck-bazel-plugin-serviceuser.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-serviceuser.yaml
@@ -6,7 +6,12 @@
             - stable-2.13
       - 'plugin-{name}-bazel-{branch}':
           branch:
-            - master
             - stable-2.16
             - stable-2.15
             - stable-2.14
+      - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
+          branch:
+            - master
+          gerrit-branch:
+            - master
+            - stable-3.0