This is a day later now, but for posterity I'll add that thanks to this thread I learned that there is a concept of "OSI approved licenses"[1], and that those licenses include MIT No Attribution License (MIT-0), and that MIT-0 is also a supported license in the GitHub UI.

It is likely I will be moving from Unlicense to MIT-0 in the future.

[1] https://opensource.org/licenses/