Juan Soto is dealing with left forearm tightness, and it would be easy to fear the worst in what’s been a train wreck of a Mets season. And one game in which the Mets offense finally awoke — for one inning, anyway — and a home run from Soto were hardly enough to ease the nerves. Still, Soto insisted the discomfort in his forearm is not a big deal after he served as the DH in an 8-0 win over Washington at Citi Field and hit his second homer of the season. It came after Carlos Mendoza said Soto felt tightness for the first time after throwing Friday. The discomfort led to an MRI, which was clean, and Mendoza said Soto — who has been limited to DH duty since coming back from a calf strain — could be in left field “in the next few days.” Tuesday, at least, he felt good enough to help the Mets pile on the Nationals, and afterward, Soto said the outburst by the Mets, most of which came in a seven-run fourth, let the Mets “remember what we’re capable of.” But they proved during his 15-game absence due to the…