Nontechnical answer...both address behavior, but personality is more permanent, harder to change, whereas disposition is more like mood, which is changeable.

A common thing to say about someone who is happy/friendly/lights up the room is "they have a sunny disposition" but they may actually be a terrible person once you know them so you could then also say "they have a sunny disposition but a terrible personality". So personality is the core behaviours you have and disposition is how the world sees you at a short glance (also I am not a psychologist). I think the meaning is slightly nuanced because it might seem like they are interchangeable but they aren't really.