I just saw Disney's 2015 Cinderella. Not a cheaply made movie, but the lead actress (naturally a brunette), whose character is supposed to be blonde, did not have her eyebrows dyed like she did her hair.
I discussed the question with a beautician who said that dying eyebrows can be a little more tricky than dying hair, but still pretty straightforward. She said the typical reason people with dark hair don't dye their eyebrows is that they look strange when they grow in with dark roots (in a way that hair doesn't). But obviously, for film, hair-and-makeup keeps the actors' hair dyed so root color doesn't appear, so they could just as readily keep up with eyebrows.
Here's the star, Lily James, eyebrows not dyed:
And, strangely, here's the brunette actress Hayley Atwell playing the brief part of her mother with eyebrows dyed to match her hair: