Fix Vertex AI hook silently discarding credentials when vertexai flag is set

[Lee-W]

Setting "vertexai": true/false in the PydanticAIVertexHook connection extra made the provider constructor call raise TypeError, since neither GoogleProvider nor GoogleCloudProvider in the currently pinned pydantic-ai accept a vertexai constructor kwarg anymore (that distinction moved to a dedicated provider class upstream). The base hook's TypeError fallback then silently re-resolved credentials from environment variables only, discarding project/location/ service_account_info/api_key with just a WARNING log line as a hint.

The field is now accepted but never forwarded to the provider constructor, so the rest of the explicit credentials still apply.

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[ColtenOuO]

Thanks! Just noticed a minor thing here:

In pydantic_ai.py:466 -- The class docstring's example JSON (Connection fields section) still includes "vertexai": true here, but the prose right below it (lines 472-473 in this PR's diff) now says the field has no effect.

Since the get_ui_field_behaviour() placeholder a few lines down (line 492) was already updated to drop vertexai, could this example be updated the same way so the two don't contradict each other?

[Lee-W]

Thanks! Just noticed a minor thing here:

In pydantic_ai.py:466 -- The class docstring's example JSON (Connection fields section) still includes "vertexai": true here, but the prose right below it (lines 472-473 in this PR's diff) now says the field has no effect.

Since the get_ui_field_behaviour() placeholder a few lines down (line 492) was already updated to drop vertexai, could this example be updated the same way so the two don't contradict each other?

Good catch! Just updated it

[ColtenOuO]

LGTM : D