docs: update GoogleSearchTool docstring to refer to Gemini models

Updates the class description of GoogleSearchTool to refer generically to 'Gemini models' rather than 'Gemini 2 models', as it applies to the broader family.

Closes #12345

Co-authored-by: Haran Rajkumar <haranrk@google.com>
PiperOrigin-RevId: 943537157

Author: haranrk

src/google/adk/tools/google_search_tool.py

@@ -31,7 +31,7 @@
 
 
 class GoogleSearchTool(BaseTool):
-  """A built-in tool that is automatically invoked by Gemini 2 models to retrieve search results from Google Search.
+  """A built-in tool that is automatically invoked by Gemini models to retrieve search results from Google Search.
 
   This tool operates internally within the model and does not require or perform
   local code execution.