Thanks, Jenny! Per your suggestion, I used:
git remote rm upstream
And this has resolved the issue for me!
For my future self / others who may end up here, here is how I came into this position. I have used upstream incorrectly - my understanding was that setting upstream is useful say if I’ve forked a repo and need to tell it where the upstream point is, i.e., the original repository. I erroneously set upstream on my own project to point at origin master, which isn’t needed, since they both point at the same place.
So the lesson for me is, the upstream shouldn't be the same place as origin.