Content style guide suggests to avoid the wrong term

[ba32107]

What article on docs.github.com is affected?

https://github.com/github/docs/blob/main/contributing/content-style-guide.md#inclusive-language

What part(s) of the article would you like to see updated?

The "Inclusive language" section suggests to avoid the term "Default branch". I think this is a mistake and this should really advise to avoid the term "Master branch".