Fix configure:invalid_usage for bgra8unorm storage

[sudonatalie]

bgra8unorm with STORAGE_BINDING is a validation error unless "bgra8unorm-storage" is enabled. Update the test to check this condition.

Spec: https://gpuweb.github.io/gpuweb/#bgra8unorm-storage

Chrome bug: https://crbug.com/565366976

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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.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located.
• Test descriptions are accurate and complete.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Tests avoid over-parameterization (see case count report).

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

[sudonatalie]

I haven't actually tested that this test now passes on an android device. If I can validate with @s-perron's new runner tomorrow I'll try that.

[github-actions]

Results for build job (at e825e04):

 Test case/subcase counts did not change.

[sudonatalie]

Since this needs a canvas and can't be run with the node runner, it's proving to be pretty cumbersome to validate. Verified it skips (though not for the right reason) and will monitor on CQ to see that it resolves the expected expectation.