Be Honest
Be forthright, but don't share so many details that you lose the job opportunity. Even if you're only looking for a temporary gig, you never know what the future holds, and you might end up enjoying the position and staying long-term. For example, say, “Right now, I'm committed to learning the ropes of the finance industry, and I hope to have a long and illustrious career in this business.” This positions you as ambitious, but not gunning for the interviewer’s job.