update types.py for tasks

Author: maxisbey

src/mcp/client/session.py

@@ -537,6 +537,8 @@ async def _received_request(self, responder: RequestResponder[types.ServerReques
             case types.PingRequest():  # pragma: no cover
                 with responder:
                     return await responder.respond(types.ClientResult(root=types.EmptyResult()))
+            case _:
+                raise NotImplementedError()
 
     async def _handle_incoming(
         self,