skew testing: Add variants.pyl owners

Follow up to crrev.com/c/2343983. Instead of hardcoding reviewers
for CL's generated by the build_weblayer_version_tests_apk_cipd_pkg
recipe we can add the --tbr-reviewers command line to the
"git cl upload" command invoked by the recipe. Then an owner
for the variants.pyl file will be added as a post submit reviewer.

R=estaab@chromium.org, mmoss@chromium.org

Bug: 1041619
Change-Id: Ic32c38670f4a05d45c1d99b550e1c29f02360373
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2373295Reviewed-by: Erik Staab <estaab@chromium.org>
Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Rakib Hasan <rmhasan@google.com>
Cr-Commit-Position: refs/heads/master@{#801620}

testing/buildbot/OWNERS

@@ -22,5 +22,11 @@ per-file chromium.webrtc.fyi.json=mbonadei@chromium.org
 # For OOBE-related test filters.
 per-file *oobe*=file://chrome/browser/ui/webui/chromeos/login/OWNERS
 
+# Owners of variants.pyl will be added as post submit reviewers to CL's
+# generated by the infra recipe build_weblayer_version_tests_apk_cipd_pkg.
+# See crbug.com/1041619.
+per-file variants.pyl=rmhasan@google.com
+per-file variants.pyl=estaab@chromium.org
+
 # TEAM: infra-dev@chromium.org
 # COMPONENT: Infra>Client>Chrome