Remove unused Tool import flagged by ruff

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wiggzz

tests/server/test_streamable_http_manager.py

@@ -291,7 +291,7 @@ async def test_stateless_requests_task_leak_on_client_disconnect():
     via httpx.ASGITransport, and simulates client disconnect by cancelling the
     request task.
     """
-    from mcp.types import CallToolResult, TextContent, Tool
+    from mcp.types import CallToolResult, TextContent
 
     tool_started = anyio.Event()
     tool_gate = anyio.Event()