Skip Occlusion query tests on Metal. Flaky on the bots. Bug: angleproject:5400 Change-Id: Ibb6ef6e16f14ee45138b99f0f549d01017c84a4f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2560559 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>