Compat: Fix depth bias test

[greggman]

Using a depthStencilAttachment requires depthWriteEnabled and depthCompare set

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

When landing this PR, be sure to make any necessary issue status updates.

[greggman]

It scares me that I somehow was able to check this in. I'm 99.999% sure I tested it but it should have failed locally before this change. It did fail locally today, before this change, I'm saying I don't know how it didn't fail back when I wrote this test.

[shrekshao]

LGTM