CTS test `inter_stage:max_variables_count,*` fails on dx12

[cwfitzgerald]

Full selectors:

• webgpu:api,validation,render_pipeline,inter_stage:max_variables_count,input:isAsync=false;builtins="all"
• webgpu:api,validation,render_pipeline,inter_stage:max_variables_count,input:isAsync=true;builtins="all"

Originally failed on trunk after landing #9101 and #9218, but the failure was waived in #9227.

https://github.com/gfx-rs/wgpu/actions/runs/23073657122/job/67029523590

[fail] webgpu:api,validation,render_pipeline,inter_stage:max_variables_count,input:isAsync=false;builtins="all" (46ms). Log:
  - (in subcase: overLimit=false) INFO: subcase ran
  - (in subcase: overLimit=true) INFO: subcase ran
  - EXCEPTION: Error: Unexpected internal error occurred: undefined
        at DeviceHolder.attemptEndTestScope (file:///D:/a/wgpu/wgpu/cts/out/webgpu/util/device_pool.js:459:13)
        at eventLoopTick (ext:core/01_core.js:179:7)
        at async DevicePool.release (file:///D:/a/wgpu/wgpu/cts/out/webgpu/util/device_pool.js:104:7)
        at async Promise.allSettled (<anonymous>)
        at async AllFeaturesMaxLimitsGPUTestSubcaseBatchState.finalize (file:///D:/a/wgpu/wgpu/cts/out/webgpu/gpu_test.js:154:21)
        at async RunCaseSpecific.run (file:///D:/a/wgpu/wgpu/cts/out/common/internal/test_group.js:694:9)
        at async file:///D:/a/wgpu/wgpu/cts/out/common/runtime/cmdline.js:218:5
[fail] webgpu:api,validation,render_pipeline,inter_stage:max_variables_count,input:isAsync=true;builtins="all" (32ms). Log:
  - (in subcase: overLimit=false) EXPECTATION FAILED: REJECTED
    Internal error in ShaderStages(VERTEX | FRAGMENT) shader: The parameter is incorrect. (0x80070057)
        at InterStageMatchingValidationTest.eventualAsyncExpectation (file:///D:/a/wgpu/wgpu/cts/out/common/framework/fixture.js:258:24)
        at InterStageMatchingValidationTest.shouldResolve (file:///D:/a/wgpu/wgpu/cts/out/common/framework/fixture.js:280:10)
        at Module.doCreateRenderPipelineTest (file:///D:/a/wgpu/wgpu/cts/out/webgpu/api/validation/validation_test_utils.js:411:9)
        at RunCaseSpecific.fn (file:///D:/a/wgpu/wgpu/cts/out/webgpu/api/validation/render_pipeline/inter_stage.spec.js:365:7)
  - (in subcase: overLimit=false) INFO: subcase ran
  - (in subcase: overLimit=true) INFO: subcase ran