Surely if you are an extra you sign some sort of release form when you take part in work for a production company? So that should explain what they are intending to do with those scans.
But If you are just blinding signing contracts without knowing what your signing then you have much bigger issues and REALLY need to get a lawyer to look over any paperwork before you sign it from now on.
Unfortunately whether we like it or not I think the future of extra work is probably not a rosy one. It won't be long before if a studio is looking to cast someone of a particular age, skin colour, height etc it will be easier and cheaper to call on an AI which will just be able to generate their extra and they don't need to pay for all the other costs that come with hiring flesh and blood people.
The website this-person-does-not-exist.com has been around since 2020 and is able to create realistic looking unique faces of people who don't exist in the real world. And with the advances in AI in the last 3 years im sure its not too far away that fully AI generated realistic looking extras will be possible without anyone's likeness even needed to be scanned.
But look its not just extras who will be out of a job due to AI and automation, there is going to be a lot of industries where the deployment of AI is going to cause certain jobs to disappear.
New technologies come along and disrupt the status quo all the time, leading job losses or even entire industries disappearing in a short space of time. I used to have a part time job when at college back in the 90s working a video rental store, and even a small town could support several of those shops back then, and now i don't even think there are any still remaining near me.
I am sure the lamp lighters, switch board operators, chimney sweeps, telegram messengers etc all felt pissed when technology eventually meant their jobs became redundant.