Adds .Rproj.user, .Rhistory, .Rdata, .httr-oauth, .DS_Store, and .quarto to
your global (a.k.a. user-level) .gitignore. This is good practice as it
decreases the chance that you will accidentally leak credentials to GitHub.
git_vaccinate() also tries to detect and fix the situation where you have a
global gitignore file, but it's missing from your global Git config.