For those that don’t know the html entity is — not &emdash; although I think in modern codebases people usually just type — directly.

This mistake does exist in the wild though: https://github.com/search?q=%26emdash%3B&type=code

If I was more ambitious I would plot the dates of the blames of these results in a histogram and see if an there is a significant increase in these mistakes (over a baseline —) correlating with the release of some models.