Elements of GPURenderPassDescriptor.colorAttachments and GPURenderPipelineDescriptor.fragment.targets should be nullable

[Norgerman]

According to WebGPU's Draft: 

• https://gpuweb.github.io/gpuweb/#dictdef-gpufragmentstate
• https://gpuweb.github.io/gpuweb/#dictdef-gpurenderpassdescriptor 

The array of colorAttachments and targets can be an array of null values. But with firefox 141 will fire an error: uncaught TypeError: GPUDevice.createRenderPipeline: Missing required 'format' member of GPUColorTargetState when doing depth only rendering on firefox which works fine on chrome.