Edited WGPUQueueWorkDoneCallbackInfo's initiliaztion in string from generate.py

[nahahahah]

The current initialization causes a compile error :

webgpu.hpp:1359:43: error: could not convert ‘{nullptr, callbackMode, cCallback, ((void*)lambda), nullptr}’ from ‘<brace-enclosed initializer list>’ to ‘wgpu::QueueWorkDoneCallbackInfo’
 1359 |                 QueueWorkDoneCallbackInfo callbackInfo = {
      |                                           ^~~~~~~~~~~~
      |                                           |
      |                                           <brace-enclosed initializer list>
  > in src/main.cpp

Opted for a per-attribute inialization. It causes no compile error.