I see this as typical of organizations that value creating a more inclusive environment for their developers.
Also, for what it's worth, Jenkins changed their terminology to use "agent" instead of slave in 2020 [0]. These efforts might seem futile in isolation, but they add up over time.
The comment I'd make is that this appears to have been settled nearly eight years ago in this particular context, and that maybe you should give it a rest.
It was "settled" in that we're all agreed it's obviously incredibly stupid but not worth fighting over and getting called racist.
The good news is that "master vs mainline" was so embarrassing that even the people who push this stuff realized they overreached and have settled down since.