Add stable-3.{3,4} gc-conductor master tree builds

Change-Id: Idedbd557d6904f5edb7419839bb9852119b5533b
diff --git a/jenkins/gerrit-bazel-plugin-gc-conductor.yaml b/jenkins/gerrit-bazel-plugin-gc-conductor.yaml
index c8e980b..2827585 100644
--- a/jenkins/gerrit-bazel-plugin-gc-conductor.yaml
+++ b/jenkins/gerrit-bazel-plugin-gc-conductor.yaml
@@ -6,6 +6,8 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.4
+            - stable-3.3
             - stable-3.2
       - 'plugin-{name}-bazel-{branch}':
           branch: