Mali does not support the robustness on Vulkan, so skip this test.

Bug: angleproject:4823
Change-Id: Id4d29fe27f10ec87d901f92ba097db9207809d42
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2331311Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>