“The Real Housewives of New York City,” Leah McSweeney, may only be a one season wonder if Bravo doesn’t cough up more cash, an insider close to the show confirmed to The Post.The breakout star and fan favorite of season 12 is being offered a “pathetically low” pay raise to appear on the next season of the reality franchise and will have to say sayonara to the series if she isn’t offered a more respectable sum, the source said.Bravo and McSweeney have not responded to The Post’s request for