Summer is traditionally regarded as a sluggish time for U.S. stocks, given the Wall Street adage: “Sell in May and go away.” This year, though, may turn out to be markedly different from past years.One reason is bullish investors are steadfastly holding on to the view that U.S. inflation is set to fall by more than the Federal Reserve forecasts, and that’s setting the stage for a possible showdown in the months ahead with policy makers, who want more interest-rate increases to push inflation back down to 2%. The S&P 500 SPX and Nasdaq Composite COMP booked their longest streak of weekly advances in years on Friday, as…