Update services/service_manager/tests/sandbox/OWNERS

They should just match //sandbox/OWNERS.

Change-Id: I98c4de76dbc05481d64893d985a29b4b6f832e97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134526Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755871}

services/service_manager/tests/sandbox/OWNERS

+file://sandbox/OWNERS
+
 per-file sandbox_win_unittest.cc=set noparent
 per-file sandbox_win_unittest.cc=file://sandbox/win/OWNERS