fix(vertex_ai): freeze the merged tool mapping to satisfy LIT002

The dict literal introduced by the previous commit is mutable-collection
construction, which put LIT002 one over its ceiling in the type-discipline gate.
Wrapping it in MappingProxyType keeps the one-shot construction Greptile asked
for while staying inside the budget: a literal passed straight to a freezing
wrapper is exempt, and ** unpacking accepts any mapping.

litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py

@@ -6,6 +6,7 @@ import time
 from collections.abc import Callable, Mapping
 from copy import deepcopy
 from functools import partial
+from types import MappingProxyType
 from typing import TYPE_CHECKING, Any, Final, Literal, Optional, Union, cast
 
 import httpx
@@ -606,7 +607,7 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
             elif "name" in tool:  # functions list
                 _input_schema = tool.get("input_schema") if tool.get("parameters") is None else None
                 _named_tool = (
-                    {**tool, "parameters": _build_vertex_schema(_input_schema)}
+                    MappingProxyType({**tool, "parameters": _build_vertex_schema(_input_schema)})
                     if isinstance(_input_schema, dict)
                     else tool
                 )