By Lisa Baertlein and Doyinsola Oladipo LOS ANGELES/NEW YORK (Reuters) – Union railworkers in the United States scored a potential key victory in their fight for improved pay and working conditions on Thursday in what could be a model for other unions. Major U.S. railroads and unions representing tens of thousands of workers reached a tentative deal after 20 hours of talks brokered by U.S. Labor Secretary Marty Walsh, averting a railway strike. While not directly applicable to ongoing negotiations at U.S. West Coast ports and upcoming talks at United Parcel Service, the rail workers’ potential…