"Typos" are acknowledged as "technical" errors, ones that obviously aren't caused by the writer's poor spelling. Although less frequent than in typing, they can also occur in handwritten texts, as a result of absent-mindedness or just an accidental stroke of the pen. Since the text wasn't actually typed, it sounds funny to call them "typos". Is there a more fitting word, one that reflects the "accidental" nature of the error?
I use the phrase slip of the pen. From Wiktionary:
(idiomatic) A mistake in handwriting.
Formally, there's always lapsus calami. From Oxford Dictionaries:
formal A slip of the pen.
Informally, you could get away with Janus Bahs Jacquet's suggestions or the like, apparently patterned after typo:
I tend to call them writos or pennos, but I doubt either is particularly well-established. (emphasis added)
Or the less specific terms mistake, error, etc. There are a lot of ways you can describe this sort of error, I think.
Lapsus is a common formalism for inadvertent error, and you could use lapsus calami specifically for writing, though it is far less common than lapsus linguae for speaking. (Wikipedia suggests lapsus clavis for keyboard errors, but that may be a step too far).
Or you could just use the English 'slip of the pen/tongue/fingers'.
mistake, spelling error, brain fart. It really is whatever you choose to name it.