Fix WebIDL error

[himorin]

from GHAction error log
This prevents updating gh-pages one.

[41](https://github.com/immersive-web/WebXR-WebGPU-Binding/actions/runs/21828933276/job/62981408526#step:3:663)
  $ pnpm add webidl2
  + webidl2 24.5.0
  Invalid Web IDL detected:
    Validation error at line 11, inside `interface XRGPUBinding -> operation createProjectionLayer -> argument init`:
      XRProjectionLayer createProjectionLayer(optional XRGPUProjectionLayerInit init);
                                                                                ^ Optional dictionary arguments must have a default value of `{}`.
    
    Validation error at line 12, inside `interface XRGPUBinding -> operation createQuadLayer -> argument init`:
      XRQuadLayer createQuadLayer(optional XRGPUQuadLayerInit init);
                                                              ^ Optional dictionary arguments must have a default value of `{}`.
    
    Validation error at line 13, inside `interface XRGPUBinding -> operation createCylinderLayer -> argument init`:
      XRCylinderLayer createCylinderLayer(optional XRGPUCylinderLayerInit init);
                                                                          ^ Optional dictionary arguments must have a default value of `{}`.
    
    Validation error at line 14, inside `interface XRGPUBinding -> operation createEquirectLayer -> argument init`:
      XREquirectLayer createEquirectLayer(optional XRGPUEquirectLayerInit init);
                                                                          ^ Optional dictionary arguments must have a default value of `{}`.
  ❌  Invalid Web IDL detected... please fix the issues above.
    
    Validation error at line 15, inside `interface XRGPUBinding -> operation createCubeLayer -> argument init`:
      XRCubeLayer createCubeLayer(optional XRGPUCubeLayerInit init);
                                                              ^ Optional dictionary arguments must have a default value of `{}`.
    
  Error: ❌  Invalid Web IDL detected... please fix the issues above.