I'm certainly not saying that there are no individual bigots in the OSS world. With thousands (millions?) of people you'll get all points of view, beneficial and toxic.
A simple 'grep' of GitHub reveals a lot of crap, but are these influential projects? Do these projects have multiple committers who have signed off with pride that "my project contains 'n-----' in the code comments"? Do these projects have lots of users?
It would be interesting to plot the occurrence of racial slurs against the number of participants in a project (controlling for offensive term filters or corpuses of 'real' language). My hunch is that the vast majority of these terms occur in one-time undergraduate projects or forgotten hobbyist repos.