I am leaning towards it being a squamous skin cancer. It's characterized by a rim of raised tissue with a dark scabby center.
There is a way to find out. Treat it as a wound, and if it grows larger instead of getting better, it's cancer.
To treat as a wound, wash well with soap and water and keep an antibiotic wound ointment on it. It should heal quickly with proper wound care. A small one like that should heal over within two weeks.
However, every "wound" like that I've seen in my flock grew larger over time instead of healing and resolving.