Build slack-integration against gerrit stable-3.6

Bug: Issue 15831
Change-Id: I87e7655ceb11f65d031abd52fd3191819e3b5c85
diff --git a/jenkins/gerrit-bazel-plugin-slack-integration.yaml b/jenkins/gerrit-bazel-plugin-slack-integration.yaml
index 628f803..2730f17 100644
--- a/jenkins/gerrit-bazel-plugin-slack-integration.yaml
+++ b/jenkins/gerrit-bazel-plugin-slack-integration.yaml
@@ -5,9 +5,10 @@
           branch:
             - master
           gerrit-branch:
+            - stable-3.6
+      - 'plugin-{name}-bazel-{branch}':
+          branch:
             - master
             - stable-3.5
             - stable-3.4
-      - 'plugin-{name}-bazel-{branch}':
-          branch:
             - stable-3.3