OWNERS: add test platform team

We co-own various cbuildbot-related packages with the CI team.

BUG=None
TEST=None

Change-Id: Iae84372c2389c01dabd01751e0f0ee211d35b6c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2616522
Reviewed-by: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
Tested-by: Sean Abraham <seanabraham@chromium.org>
diff --git a/OWNERS b/OWNERS
index 98eb462..b629c22 100644
--- a/OWNERS
+++ b/OWNERS
@@ -1,5 +1,6 @@
 include /OWNERS.build
 include /OWNERS.ci
+include /OWNERS.testplatform
 
 per-file OWNERS.au = file://OWNERS.au
 per-file OWNERS.kernel = file://OWNERS.kernel