By David Shepardson WASHINGTON (Reuters) -A group of 21 states led by Florida on Tuesday asked a U.S. judge to block a federal COVID-19 mandate requiring masks on airplanes and other forms of transportation. The lawsuit is the latest in a series of recent legal challenges to a Centers for Disease Control and Prevention (CDC) public health order and Transportation Security Administration (TSA) directive that have been in place since February 2021 covering airports, trains, buses, ride-share vehicles and transit hubs. The administration of President Joe Biden said earlier this month it would ext…