When Australia’s George Miller came here in 2016 to serve as jury president, just months after his “Mad Max: Fury Road” won six Oscars, he swept in like a conquering hero. His movie was undeniable: a reinvigoration of both his career and the action genre. Often, the relationship between Cannes and the blockbuster directors it invites comes off as strained — see French artist Zaho de Sagazan serenading this year’s jury president Greta Gerwig at Tuesday’s opening ceremony — but with Miller, the moment felt right. Things change. His “Furiosa: A Mad Max Saga” (in cinemas May 24), a somewhat dutifu…