That’s one way to slay a red carpet. Lena Dunham returned to the Met Gala red carpet on Monday for the first time in seven years — in a dress inspired by a 17th century beheading. The “Girls” creator, 39, wore a custom crimson gown by Valentino’s Alessandro Michele, embroidered with sequins and trimmed with crow’s feathers that encircled the high neckline and ran down the end of the long train. Lena Dunham’s custom Valentino gown for the 2026 Met Gala was based on a “particular blood spatter” in a 17th-century beheading painting. Getty Images The artwork behind the look: Artemisia Gentileschi’s circa-1620 masterwork “Judith Slaying Holofernes.” Corbis via Getty Images Designer Alessandro Michele keyed into the gory detail to create the gown, which featured crimson crow’s feathers and all-over sequins.…