By David Lawder WASHINGTON (Reuters) -U.S. Treasury Secretary Janet Yellen said on Wednesday that inflation would not be a decade-long problem for the United States and that the Biden administration’s COVID-19 rescue spending contributed only “modestly” to price hikes. Yellen, fielding questions from lawmakers on high inflation for a second straight day, said that recent readings above 8% were “unacceptable” for the United States and a 2% inflation target is an “appropriate target” for the Federal Reserve. “I see no way in which inflation is a decade-long…matter,” Yellen told the U.S. House …