Cannot use hub pr checkout after PR was updated

[nh2]

Command attempted:

$ hub pr checkout 1234

# now somebody force-pushes the PR to incorporate feedback

$ hub pr checkout 1234
fatal: Refusing to fetch into current branch refs/heads/mybranch of non-bare repository

What happened:

hub fails with an internal git error.

As a user I want to get the new changes from the PR with the incorporated feedback.

hub should either do that, or tell me why I somehow can't get that (and perhaps actionable infon on what I should do instead), instead of failing with an internal git error message.

More info:

git version 2.23.1
hub version 2.12.7

on NixOS Linux 19.09.

[nh2]

A workaround seems to be to git checkout another branch, then git branch -D mybranch to delete the branch hub had created, and using hub pr checkout 1234 again so that it recreates it.

[mislav]

Duplicate of #2061