chore(deps): Fix typo in package dependency name (#2018)

Partially reverts #2011 to fix the typo in the
package name.

The original PR breaks builds due to incorrect package name.

<img width="2254" height="522" alt="image"
src="https://github.com/user-attachments/assets/d51aba16-a84e-46cb-b17c-4eab1576dd59"
/>

Author: anubhav756

docs/en/getting-started/quickstart/python/langchain/requirements.txt

@@ -1,5 +1,5 @@
 langchain==1.0.8
-llangchain-google-vertexai==3.0.3
+langchain-google-vertexai==3.0.3
 langgraph==1.0.3
 toolbox-langchain==0.5.3
 pytest==9.0.1