Build project-group-structure against gerrit stable-3.6

Bug: Issue 15831
Change-Id: Ic3d7079d4ac40f67f570c4ce0b6caa87a3fceb58
diff --git a/jenkins/gerrit-bazel-plugin-project-group-structure.yaml b/jenkins/gerrit-bazel-plugin-project-group-structure.yaml
index 706e828..c393e1d 100644
--- a/jenkins/gerrit-bazel-plugin-project-group-structure.yaml
+++ b/jenkins/gerrit-bazel-plugin-project-group-structure.yaml
@@ -9,5 +9,6 @@
           branch:
             - master
           gerrit-branch:
+            - stable-3.6
             - stable-3.5
             - stable-3.4