Both are right. The first is an alternate, older form. We have others like "spelt" that some people still say, too, instead of "spelled." Language is dynamic, always changing. Currently, we have "dived" as an alternate for "dove." This isn't very unusual, really.
I would say that I don't have "learnt" in my speech, so I would recommend "learned." Also, since you are using it as an attri