Build automerger plugin on its own stable-2.16 branch

Change-Id: Icaa2f32d0d6377b32312b19430c4e67c18edd9bd
diff --git a/jenkins/gerrit-buck-bazel-plugin-automerger.yaml b/jenkins/gerrit-buck-bazel-plugin-automerger.yaml
index bba5019..beca10f 100644
--- a/jenkins/gerrit-buck-bazel-plugin-automerger.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-automerger.yaml
@@ -7,8 +7,8 @@
           gerrit-branch:
             - master
             - stable-3.0
-            - stable-2.16
       - 'plugin-{name}-bazel-{branch}':
           branch:
+            - stable-2.16
             - stable-2.15
             - stable-2.14