fix: correct Context[None] to bare Context in test_list_roots_callback

Same rationale as the previous commit: this server has no lifespan argument,
so the default lifespan yields {} typed dict[str, Any]. Context[None] types
lifespan_context as None, which is factually wrong — it only passed
type-check because the test never dereferences it.

Author: maxisbey

tests/client/test_list_roots_callback.py

@@ -25,7 +25,7 @@ async def list_roots_callback(
         return callback_return
 
     @server.tool("test_list_roots")
-    async def test_list_roots(context: Context[None], message: str):
+    async def test_list_roots(context: Context, message: str):
         roots = await context.session.list_roots()
         assert roots == callback_return
         return True