CQ: Add linux_ubsan to default trybots.

Since it's now green.

BUG=webrtc:5124
R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1740973002 .

Cr-Commit-Position: refs/heads/master@{#11784}
diff --git a/infra/config/cq.cfg b/infra/config/cq.cfg
index 7708618..eb176ea 100644
--- a/infra/config/cq.cfg
+++ b/infra/config/cq.cfg
@@ -49,6 +49,7 @@
       builders { name: "linux_msan" }
       builders { name: "linux_rel" }
       builders { name: "linux_tsan2" }
+      builders { name: "linux_ubsan" }
       builders { name: "linux_ubsan_vptr" }
       builders { name: "mac_asan" }
       builders { name: "mac_baremetal" }