Upgrade a suppression from RetryOnFailure to Failure

This flakes enough times in a row that RetryOnFailure is not enough.
Could be because the flake rate is high, or because some system state
causes it to fail consistently across a few retries.

No-Try: true
TBR: kbr@chromium.org
Bug: 1112101, angleproject:4922
Change-Id: I1e5612644349ac28e782ef25ede61a2eac255631
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2338857Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795102}

content/test/gpu/gpu_tests/test_expectations/webgl_conformance_expectations.txt

@@ -154,7 +154,8 @@ crbug.com/angleproject/2914 [ vulkan passthrough ] conformance/textures/misc/tex
 crbug.com/angleproject/4931 [ win nvidia vulkan passthrough ] conformance/textures/misc/texture-mips.html [ Failure ]
 
 # Win / Intel / Vulkan / Passthrough command decoder
-crbug.com/angleproject/4922 [ win intel vulkan passthrough ] conformance/context/context-attributes-alpha-depth-stencil-antialias.html [ RetryOnFailure ]
+# Technically flaky, but flake rate is too high for RetryOnFailure.
+crbug.com/angleproject/4922 [ win intel vulkan passthrough ] conformance/context/context-attributes-alpha-depth-stencil-antialias.html [ Failure ]
 
 ####################
 # Fuchsia failures     #