Build ref-copy against gerrit stable-3.6

Bug: Issue 15831
Change-Id: I3c7977baf1b214a7e042a6b5264b70e51fa286f5
diff --git a/jenkins/gerrit-bazel-plugin-ref-copy.yaml b/jenkins/gerrit-bazel-plugin-ref-copy.yaml
index 4824acb..02f5e4a 100644
--- a/jenkins/gerrit-bazel-plugin-ref-copy.yaml
+++ b/jenkins/gerrit-bazel-plugin-ref-copy.yaml
@@ -6,6 +6,7 @@
             - main
           gerrit-branch:
             - master
+            - stable-3.6
             - stable-3.5
             - stable-3.4
             - stable-3.3