text: Title: VertexAIRegion List Incorrect
  Body: ### Initial Checks
  
  - [x] I confirm that I'm using the latest version of Pydantic AI
  
  ### Description
  
  In the documentation, I think the [VertexAIRegion](https://ai.pydantic.dev/api/models/vertexai/#pydantic_ai.models.vertexai.VertexAiRegion) list should point to the following url instead: [Generative AI on Vertex AI locations](https://cloud.google.com/vertex-ai/generative-ai/docs/learn/locations#genai-locations), and remove regions not listed on that site.
  
  When I was working on implementing the VertexAIModel in my project I wanted to use `us-west2` as it is the region closest to me with the lowest latency, however in doing so I get the following error message:
  
  ```
  pydantic_ai.exceptions.UnexpectedModelBehavior: Unexpected response from gemini 404, body:
  {
    "error": {
      "code": 404,
      "message": "Publisher Model `projects/gen-lang-client-0404328887/locations/us-west2/publishers/google/models/gemini-2.0-flash` not found.",
      "status": "NOT_FOUND"
    }
  }
  ```
  
  What I've found is you have to use a region listed here: [Generative AI on Vertex AI locations](https://cloud.google.com/vertex-ai/generative-ai/docs/learn/locations#genai-locations). In my case, using `us-west4` I do not get any errors.
  
  Maybe I'm doing something wrong?
  
  ### Example Code
  
  ```Python
  
  ```
  
  ### Python, Pydantic AI & LLM client version
  
  ```Text
  Python 3.10.12
  
  pydantic-ai-0.0.30
  
  Gemini via VertexAI
  ```