Fix intra-invocation coherence 3d tests (#3521)

* Coordinates for 3D textures currently use 1 for the z component
  instead of 0, but the texutre is always created with a depth of 1 so
  this is out of bounds

src/webgpu/shader/execution/memory_model/texture_intra_invocation_coherence.spec.ts

@@ -39,7 +39,7 @@ fn indexToCoord(idx : u32) -> vec2u {
     case '3d': {
       return `
 fn indexToCoord(idx : u32) -> vec3u {
-  return vec3u(idx % (wgx * num_wgs_x), idx / (wgx * num_wgs_x), 1);
+  return vec3u(idx % (wgx * num_wgs_x), idx / (wgx * num_wgs_x), 0);
 }`;
     }
     default: {