Skip AF Matrix pair operation CTS

Skipping these tests, because they are very slow. Will re-enable once
their performance is improved upstream.

BUG=tint:2051

Change-Id: I809b186ff304b33c2e75b83fc13e94783a114304
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/154701
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
diff --git a/webgpu-cts/expectations.txt b/webgpu-cts/expectations.txt
index ea1ed82..d0b8d37 100644
--- a/webgpu-cts/expectations.txt
+++ b/webgpu-cts/expectations.txt
@@ -852,6 +852,14 @@
 crbug.com/tint/2035 [ webgpu-dxc-enabled win10 ] webgpu:shader,validation,expression,call,builtin,tan:values:stage="override";type="vec4%3Cf16%3E" [ Failure ]
 
 ################################################################################
+# Abstract matrix by matrix operations
+# Skipped because they are very slow and cause general timeouts
+# KEEP
+################################################################################
+crbug.com/tint/2051 webgpu:shader,execution,expression,binary,af_matrix_addition:* [ Skip ]
+crbug.com/tint/2051 webgpu:shader,execution,expression,binary,af_matrix_subtraction:* [ Skip ]
+
+################################################################################
 # untriaged DXC failures
 ################################################################################
 crbug.com/tint/0000 [ intel-0x9bc5 win10 ] webgpu:api,operation,command_buffer,queries,occlusionQuery:occlusion_query,basic:writeMask=0;renderMode="direct";bufferOffset="zero";querySetOffset="non-zero" [ Failure ]