MOSCOW — A Russian court on Tuesday rejected an appeal by U.S. basketball star Brittney Griner of her nine-year prison sentence for drug possession, a step that could move her closer to a possible high-stakes prisoner swap between Moscow and Washington.The eight-time all-star center with the WNBA’s Phoenix Mercury and a two-time Olympic gold medalist was convicted Aug. 4 after police said they found vape canisters containing cannabis oil in her luggage at Moscow’s Sheremetyevo Airport.Griner, 31, was not …