Add stip@ to testing/buildbot/OWNERS.

BUG=

Review-Url: https://codereview.chromium.org/2152413003
Cr-Commit-Position: refs/heads/master@{#406029}

testing/buildbot/OWNERS

@@ -9,10 +9,10 @@ machenbach@chromium.org
 maruel@chromium.org
 phajdan.jr@chromium.org
 sky@chromium.org
+stip@chromium.org
 thakis@chromium.org
 
 per-file chromium.android.json=jbudorick@chromium.org
-per-file chromium.android.json=stip@chromium.org
 
 # For Site Isolation FYI tests:
 per-file chromium.fyi.json=creis@chromium.org