inline source code for overfitting plots

[simonpcouch]

A little bit of developer complexity for the sake of participant simplicity. Given that we're already teaching a binary classification problem, I thought it'd be nice if the colors matched the ones that participants would expect with the example plot, i.e. green and tan mean two levels of an outcome variable.

Source for the original image: https://github.com/topepo/2022-nyr-workshop/blob/19266c8254a7c53b7a29bf424e4cafcbab91d5b5/5-tuning.Rmd#L173C1-L276C4