WebGPUExpectations: temp suppressions for limit changes

WebGPU limits for maxColorAttachments and maxStorageTexturePerStage are
being changed. The test are suppressed during the change to allow Dawn
CLs to go through. Suppressions will be removed when the CTS is fixed.

Bug: dawn:796
Change-Id: Ie1beed16b7137a110098059f5b410bfa5c77e85c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2987838


Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#896042}