I don’t know if this constitutes a spoiler, but it might just count as news: The latest Marvel movie, “Eternals,” actually features a sex scene. It’s pretty short (the scene, not the movie) and not particularly steamy, which has less to do with the chemistry of the participants than the chilly-looking riverbank they’ve chosen for the occasion. We’re in Babylon circa 575 B.C., and Ikaris (Richard Madden) and Sersi (Gemma Chan), immortal beings known as Eternals, are expressing their love not just for each other but also for the planet they will spend the next several thousand years trying to protect. Happily, director Chloé Zhao seems to have resisted the temptation to film them writhing on a beach, perhaps aware that she isn’t making “From Here to Eternals.”