IT’S SPRING, which means it’s time for us to revisit that annual ritual known as the “Scrubs” Renewal Discussion. After NBC finally cut it loose last year, you’ve got to give credit to Zach Braff and company for surviving the transplant to ABC. By our lights, the show has gotten even funnier. Still, it seems that Quick-Edit Comedies (from “Arrested Development” to “30 Rock”) are doomed never to make it really big, and “Scrubs” is no different, pulling a meager 5 million viewers per episode. According to TV Series Finale, the show’s stars have made it clear that the next season, if it happens, would be the last. And ABC execs know that those 5 million viewers are faithful – which these days may be the only defense against an unstoppable “American Idol.” Will the patient survive? Trade with caution in perhaps the toughest renewal market this year.