I'm going to disagree with the other answers telling you to not raise the issue and to stick it out.
You have a field of interest, which is machine learning. You were brought into this company to work on a machine learning project. Your boss, who is on the machine learning team, is not your supervisor, who is the project lead for this other project you're now on, and that's a problem (it's always a problem when your boss and your supervisor are not the same person).
To me, it sounds like your job description has changed without your knowledge or approval, and that's a problem. What I would do is the following:
1) Raise this issue with your boss (not your supervisor, he doesn't care). Explain, politely but strongly, that you were hired as a machine learning intern, and you really want to work on a machine learning project. Explain that you know business needs change and so on, but emphasize this is what was advertised and you'd really like to do that.
2) Ask your boss how long you are expected to be "on loan" for this other project. He should have an understanding of your responsibilities and should have planned for your work over your internship, so he should be able to tell you if this is a temporary thing or if your internship as you believed it is over. Once again, emphasize that you want to work on machine learning stuff and that is your primary focus.
3) Once this is done, then you go along with whatever your boss decides. He has been made aware of the issue; you want to do this one thing and you're not doing that thing, so you're less than happy. His goal should be to make you happy (as long as it aligns with business objectives), so he should be preparing to bring you off that other project and back to your main focus as soon as possible. Trust him to make you happy, if not now, then in the near future.
A side note to all of this is that companies like interns. Basically, you're cheap labour. Even if you're making the same salary as a regular employee, the company is likely getting some form of kickback from the government, your school, or whatever, for hiring you instead of a regular employee. They like that kickback. They don't want you to go back to school and tell all your friends that this company sucks and the work is boring and they don't care about the interns, etc, because then they lose the cheap labour. So they want to make you happy. If you let them know they are not happy, they will do their best to make you happy (modulo business concerns) because they want you to be happy. So stick it out, but also make it known that you are not happy; if you don't say you're not happy then they won't know you're not happy and nothing will be done.
Side note about machine learning: ML is hard. Even the so-called "experts" in ML more or less have no idea how it works under the hood. The field is really in its infancy right now, and anyone who tells you they're doing something big and fancy with ML is really probably just using a third-party big data NLP analyzer to do some mundane task with a best-case 40% correctness ratio, unless we're talking about a Google-level scale. It's unlikely your company is really doing something cool with ML unless they are Google-level, because really nobody knows how to do anything cool with ML right now, and doing something cool with ML requires at least postgrad, and sometimes post-doctoral, levels of expertise in the field. I presume you're an undergrad right now, and based on that, there are a couple explanations for what you're going through:
1) ML is too hard for you, where you are right now. If they were to truly bring you into an ML project, you would be lost in the weeds within an hour. It's not worth the effort it would take to train an undergrad on the finer details of ML, so instead they're putting you where you can actually make an impact. Be thankful for this.
2) The company really isn't doing anything cool with ML; they're doing a bunch of small investigations into various tools and approaches, but that work is short and sporadic, and right now there isn't anything to be done that the company needs. So rather than saddling you with "busy work" in ML, they're putting you on something meaningful. Be thankful for this.
So make it known that you want to learn about ML, and doing ML work would make you happy. But realistically there are probably 2 blockers here, both your experience level and also your company's expertise, which are blocking you from doing what you really want to do, and there's not a ton you can do about either of those.