LIVERPOOL—More than 60 years ago, four boys from Liverpool changed the music world forever. This Saturday, the music world returns to Liverpool to crown the winner of the 2023 Eurovision Song Contest, the longest-running televised music competition in the world, one even older than the Beatles. How big is Eurovision? Big enough that railway unions have decided to go on strike on Saturday, the day of the final, putting it on a par with the other event that the unions have decided to disrupt: the FA Cup final next month between Manchester City and Manchester United. Eurovision began in 1956...