March 2 (Reuters) - Gold prices edged higher on Tuesday as a retreat in U.S. Treasury yields and optimism over the $1.9 trillion coronavirus relief bill lifted the allure of the non-yielding metal. * Benchmark U.S. Treasury yields eased further from a one-year high hit last week as Federal Reserve officials continued to downplay runaway inflation concerns. * The European Central Bank slowed its net purchases of debt last week even as borrowing costs jumped in the financial markets, casting a shadow over a nascent recovery in the pandemic-stricken euro zone economy.