Build zuul-results-summary against gerrit stable-3.6

Bug: Issue 15831
Change-Id: If869d95b41366dc97cf4fe4562b9ad088bd12612
diff --git a/jenkins/gerrit-bazel-plugin-zuul-results-summary.yaml b/jenkins/gerrit-bazel-plugin-zuul-results-summary.yaml
index 7221e70..c8b0c73 100644
--- a/jenkins/gerrit-bazel-plugin-zuul-results-summary.yaml
+++ b/jenkins/gerrit-bazel-plugin-zuul-results-summary.yaml
@@ -6,6 +6,7 @@
             - main
           gerrit-branch:
             - master
+            - stable-3.6
             - stable-3.5
             - stable-3.4
             - stable-3.3