Add stable-2.12 and stable-2.13 branches to ci for its-phabricator

Change-Id: I93a048116dcbdc51e81a752a5fa76e32f5a697d9
diff --git a/jenkins/gerrit-buck-plugin-its-phabricator.yaml b/jenkins/gerrit-buck-plugin-its-phabricator.yaml
index 8b1fca6..60d3f39 100644
--- a/jenkins/gerrit-buck-plugin-its-phabricator.yaml
+++ b/jenkins/gerrit-buck-plugin-its-phabricator.yaml
@@ -2,6 +2,8 @@
     name: phabricator
     branch:
       - master
+      - stable-2.13
+      - stable-2.12
     jobs:
       - 'plugin-its-{name}-{branch}'