By Andy Bruce and David Milliken LONDON (Reuters) – Bond investors were unconvinced by British Prime Minister Liz Truss’s partial reversal of her economic plan on Friday, as gilts gave up early gains to end the day down sharply, especially for long-dated bonds. As of 1546 GMT, long-dated gilt yields were more than 20 basis points up on the day, having fallen almost 30 basis points in early trading – another huge intraday swing that underlines the volatility facing gilt market players. While U.S. and German government bonds also erased their gains during the day, long-dated British debt again u…