John Maine (pictured) told The Post after tonight’s loss to the Astros that he expects to have arthroscopic surgery after the season to remove a painful bone spur in his right shoulder. Maine, who gave up a season-high eight earned runs in the 8-3 setback, plans to pitch through the pain — with the Mets’ blessing — for the rest of the season, then have the surgery. “Something’s going to have to be done,” Maine said. We will have more on this and all of Maine’s arm woes in Sunday’s edition of The Post. …