By Jorge Nieto and Lizbeth Diaz TIJUANA, Mexico (Reuters) – The number of Ukrainians arriving at the U.S.-Mexico border to seek asylum in the United States since Russia’s invasion of its neighbor has more than doubled in less than a week, officials said. Lying on plastic mattresses, hundreds of Ukrainians including families waited in a crowded shelter run by the local government in the Mexican border city of Tijuana this week. Enrique Lucero, director of the city’s immigration services, said about 2,829 Ukrainians were waiting, more than double the 1,200 counted last Friday. Nearly two-thirds …