Add ART's Bug Component ID to `test/OWNERS` file.

As per go/xts-owners-policy.

Test: Rely on TreeHugger/AyeAye
Bug: 261015566
Change-Id: Ib34b984c8d1afe92be306091823b1a4f3e29db26
diff --git a/test/OWNERS b/test/OWNERS
index 7d11748..2e4627e 100644
--- a/test/OWNERS
+++ b/test/OWNERS
@@ -1,3 +1,4 @@
+# Bug component: 86431
 # See also ART owners in the parent directory.
 rpl@google.com
 dsrbecky@google.com