fix review comment

Author: seratch

src/agents/models/openai_responses.py

@@ -477,9 +477,10 @@ def _convert_tool(cls, tool: Tool) -> tuple[ToolParam, ResponseIncludable | None
                     "filters": tool.filters.model_dump() if tool.filters is not None else None,
                     "user_location": tool.user_location,
                     "search_context_size": tool.search_context_size,
-                    "external_web_access": tool.external_web_access,
                 },
             )
+            if tool.external_web_access is not None:
+                converted_tool["external_web_access"] = tool.external_web_access
             includes = None
         elif isinstance(tool, FileSearchTool):
             converted_tool = {