How can I set a timeout for a locked table in Function ?

CREATE OR REPLACE FUNCTION public."testlock"()
    RETURNS TABLE
	(
		 id integer,
		 name character varying, 
		 state integer, 
		 owner character varying
	) 
    LANGUAGE 'plpgsql'
AS $BODY$	
	 BEGIN	
	 	SET  "statement_timeout" = 6000; --- It's not changing. !!
		LOCK TABLE public."lock" IN ROW EXCLUSIVE MODE;	
				UPDATE public."lock" as l set name = 'deneme' WHERE l."id" = 4;	
	
		RETURN QUERY 
			select l."id",l."name",l."state",l."owner" from public."lock" as l, pg_sleep(10) where l."id" = 4;		
	END; 
$BODY$;

select * from public."testlock"(); 

How can I do ?