A dictionary first and foremost tells you the use/meaning today. You need to look into the etymology to understand if it has something to do with slavery.
And yet not many people do or seem to care. Why? You might say it's because our culture is still not enlightened, but it really is just because it doesn't matter what the usage used to be as long as it's used with a different, more-or-less harmless meaning today. Not only that, but what about words that have had countless interpretations since forever (black/white)? Why pick the one that happens to be racist?
And I may be making a wild conjecture here, but it's not like talking about a "master branch" will make you more likely to become pro-slavery. I mean, what would "master branch" even mean out of the context of version control?
Words are just labels to meaning. It makes no sense to care about the label. People have declared love with N-words and advocated for genocide with flowery language. Banishing words is a prime example of bikeshedding.
stop being mean. you shouldn't impose your control. whip me for telling you not to. and scold them for whipping me. decentralize the git commit hierarchy! no order!