Mark unreachable catch-all case as excluded from coverage

Author: maxisbey

src/mcp/client/session.py

@@ -582,7 +582,7 @@ async def _received_request(self, responder: RequestResponder[types.ServerReques
                 with responder:
                     return await responder.respond(types.ClientResult(root=types.EmptyResult()))
 
-            case _:
+            case _:  # pragma: no cover
                 pass  # Task requests handled above by _task_handlers
 
         return None