Add per-file autoninja_test.py=file://BUILD_OWNERS to tests/OWNERS

Change-Id: I0f2edc79ba52296d21a8303608c3231cb87bae4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5568703
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Auto-Submit: Junji Watanabe <jwata@google.com>

tests/OWNERS

@@ -1,5 +1,5 @@
 per-file autoninja_test.py=brucedawson@chromium.org
-per-file autoninja_test.py=tikuta@chromium.org
+per-file autoninja_test.py=file://BUILD_OWNERS
 per-file bazel_test.py=file://CROS_OWNERS
 per-file ninjalog_uploader_test.py=tikuta@chromium.org
 per-file ninja_reclient_test.py=file://BUILD_OWNERS