Although I enjoy this sort of music, I haven't ever performed it, and have only "studied" bits that come up as examples in composition texts. I can tell you the key that it is written in, and that it ends on with a major chord, even though it is written in a minor key, and I can, as you have, count the instance of the accidental. Those are superficialities.

Why it is there is a different question, and requires reflection on the motion of the piece, a bit of understanding of the musical conventions of the genre, and a certain amount of speculation.

There are some who maintain, for instance, that there was a tendency to sharp a note in order to create a major rather than minor harmony because using the intonation of the time, the major sounded better. Some will point our that the note may be a product of voice leading and would argue that it is foreground detail and the focus should be on the underlying root progression syntax(!)

I am slightly embarrassed to admit that I know what that means, at least sort of, but that kind of discussion is above my pay grade--