Add support for stable-3.13 in gerritPipeline.groovy

Change-Id: I21f19c862df1eb83cd680315782e4e396eafa0b5
diff --git a/vars/gerritPipeline.groovy b/vars/gerritPipeline.groovy
index 4de5d25..660ea84 100644
--- a/vars/gerritPipeline.groovy
+++ b/vars/gerritPipeline.groovy
@@ -130,7 +130,7 @@
 
 def collectBuildModes() {
     Builds.modes = []
-    if (env.GERRIT_BRANCH == "master" || env.GERRIT_BRANCH ==~ /stable-3.1[0-2]/) {
+    if (env.GERRIT_BRANCH == "master" || env.GERRIT_BRANCH ==~ /stable-3.1[0-3]/) {
         Builds.modes = ["notedb", "rbe"]
     } else {
         throw new Exception("Unsupported branch ${env.GERRIT_BRANCH}")