Build its-base plugin on stable-3.4 branch

Change-Id: Ieab5f3e90717743a3cfe573d3b513eaec004a2b3
diff --git a/jenkins/gerrit-bazel-plugin-its-base.yaml b/jenkins/gerrit-bazel-plugin-its-base.yaml
index 4360dd63..788b6a2 100644
--- a/jenkins/gerrit-bazel-plugin-its-base.yaml
+++ b/jenkins/gerrit-bazel-plugin-its-base.yaml
@@ -6,6 +6,7 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.4
             - stable-3.3
           targets: 'plugins/its-base:its-base plugins/its-base:its_base_tests'
       - 'plugin-{name}-bazel-{branch}':