WASHINGTON — The Supreme Court ruled decisively in favor of a death-row inmate in Georgia today, chastising state prosecutors for improperly keeping African-Americans off the jury that convicted him of killing a white woman.The justices ruled 7-1 in favor of death row inmate Timothy Tyrone Foster in underscoring the importance of rules they laid out in 1986 to prevent racial discrimination in the selection of juries.Chief Justice John G. Roberts Jr. wrote for the court that Georgia “prosecutors were motivated …