Master branch refers to a master copy, like in the recording industry. While I'm very much in favor of removing symbolism that evokes past injustice, this feels misguided to me.
It has nothing to do with the master/slave terminology, which does come up in the context of database replication and which should certainly be removed from CS textbooks.
The words mean what we understand them to mean. Like the Hacker in Hacker News. I doubt it was intended to mean “one who breaks into computers” even if the majority of people seem to have adopted that meaning.
I’ve never thought of master in this context as anything other than like a recording master. It doesn’t give orders to anything or anybody, it just represents your best version of truth.
It has nothing to do with the master/slave terminology, which does come up in the context of database replication and which should certainly be removed from CS textbooks.