WASHINGTON — A deeply divided Supreme Court upheld the use of a controversial drug in lethal-injection executions today, even as two dissenting justices said for the first time it’s “highly likely” the death penalty itself is unconstitutional.Trading sharp words on their last day together until the fall, the justices voted 5-4 in a case from Oklahoma that the sedative midazolam can be used in executions without violating the Eighth Amendment prohibition on cruel and unusual punishment.The drug was …