[owners] Make test/ owned by COMMON_OWNERS

Adding and improving tests should have as little friction
as possible.

Change-Id: I61c09ccadf12b7367979fbf3b8cb97a64e0c70bc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1648243
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62038}

test/OWNERS

-file://INFRA_OWNERS
+file://COMMON_OWNERS