By Marianna Parraga and Matt Spetalnick WASHINGTON (Reuters) – Venezuela’s opposition parties have warned they are likely to withdraw backing for Juan Guaido’s Washington-endorsed interim government in 2023, four people familiar with the matter said, raising questions about the future of the country’s overseas holdings. Guaido has been the public face of the country’s opposition since the United States and many other governments rejected President Nicolas Maduro’s 2018 re-election as a sham. But most opposition representatives visiting Washington this week told U.S. officials they would not co…