OWNERS: allow copybara to update common.mk automatically

BUG=None
TEST=CQ passes

Change-Id: I50b40b825107b586d7fdf74587364082204ee27e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/audiotest/+/6475624
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Commit-Queue: Yu-Hsuan Hsu <yuhsuan@chromium.org>

OWNERS

diff --git a/OWNERS b/OWNERS
index 06d7786..009e1dd 100644
--- a/OWNERS
+++ b/OWNERS
@@ -2,3 +2,6 @@
 
 cychiang@chromium.org
 yuhsuan@chromium.org
+
+# Robots.
+per-file common.mk = file:chromiumos/owners:v1:/bots/OWNERS.copybara