google-genai[patch]: on_llm_new_token fix (#16924)

### This pull request makes the following changes:
* Fixed issue #16913

Fixed the google gen ai chat_models.py code to make sure that the
callback is called before the token is yielded

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---------

Co-authored-by: Erick Friis <[email protected]>

libs/partners/google-genai/langchain_google_genai/chat_models.py

@@ -598,6 +598,7 @@ def _stream(
         for chunk in response:
             _chat_result = _response_to_result(chunk, stream=True)
             gen = cast(ChatGenerationChunk, _chat_result.generations[0])
+
             if run_manager:
                 run_manager.on_llm_new_token(gen.text)
             yield gen
@@ -622,6 +623,7 @@ async def _astream(
         ):
             _chat_result = _response_to_result(chunk, stream=True)
             gen = cast(ChatGenerationChunk, _chat_result.generations[0])
+
             if run_manager:
                 await run_manager.on_llm_new_token(gen.text)
             yield gen