docs(docs): correct package name from langchain-google_vertexai to langchain-google-vertexai for VertexAILLM (#32095)

- **Description:** This PR updates the `package` field for the VertexAI
integration in the documentation metadata. The original value was
`langchain-google_vertexai`, which has been corrected to
`langchain-google-vertexai` to reflect the actual package name used in
PyPI and LangChain integrations.
  - **Issue:** N/A
  - **Dependencies:** None
  - **Twitter handle:** N/A

Author: bansalkanav

docs/src/theme/FeatureTables.js

@@ -322,7 +322,7 @@ const FEATURE_TABLES = {
             {
                 name: "VertexAILLM",
                 link: "google_vertexai",
-                package: "langchain-google_vertexai",
+                package: "langchain-google-vertexai",
                 apiLink: "https://python.langchain.com/api_reference/google_vertexai/llms/langchain_google_vertexai.llms.VertexAI.html"
             },
             {