`Computepass Encoding` benchmark fails on devices without RW R32F support

[cwfitzgerald]

Discovered in #8610 (comment)

        FAIL [   1.492s] wgpu-benchmark::bench/wgpu-benchmark Computepass Encoding
  stdout ---
    Running benchmark: Computepass Encoding
      Using adapter: Apple A9 GPU (Metal)
  stderr ---

    thread 'main' panicked at wgpu\src\backend\wgpu_core.rs:1251:26:
    wgpu error: Validation Error

    Caused by:
      In Device::create_bind_group
        The adapter does not support read-write access for storage textures of format R32Float