It’s amusing to watch Steve Carrell and Steve Buscemi strut around in jeweled costumes, tossing their lion-mane hair to and fro. It’s also funny to watch Jim Carrey play an over-the-top Criss Angel wannabe. Sadly, these are the only highlights in “The Incredible Burt Wonderstone,” a slow, humdrum comedy that would have worked better as a 10-minute sketch than a feature film. Because the performers are charismatic, director Don Scardino is able to milk a few laughs from the tepid, committee-written screenplay, but that’s hardly an endorsement.