Is it very noticeable? if it's really faint and only a few cuts I don't think anybody will notice, but if your whole arm is covered with them and noticeable from a few feet away you probably want to cover them up. Even if they don't say anything, a lot of people will be disturbed, there is so much social stigma and ignorance about self injury. So if you go bare armed, plan to be stared at uncomfortably the whole day. (which is ok if you can deal with it, I just dont think I could)
If you want to cover them up you can use any kind of thin long-sleeved shirt inside or sun blocking sleeves and say you have sun allergy/embarrassing moles/birthmarks if anyone asks. concealer won't work if your scars are noticeable enough to need to be covered up
Congrats on your new job and good luck