Build healthcheck plugin on stable-3.4

Change-Id: I3315a31571daca40b9f053e2594f3129fe1d4289
diff --git a/jenkins/gerrit-bazel-plugin-healthcheck.yaml b/jenkins/gerrit-bazel-plugin-healthcheck.yaml
index 9b9e899..45d809b 100644
--- a/jenkins/gerrit-bazel-plugin-healthcheck.yaml
+++ b/jenkins/gerrit-bazel-plugin-healthcheck.yaml
@@ -8,3 +8,8 @@
             - stable-3.2
             - stable-3.1
             - stable-2.16
+      - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
+          branch:
+            - master
+          gerrit-branch:
+            - stable-3.4