There’s no need to create that pr-8142 branch, which will otherwise hang around indefinitely which is most commonly not what you want:

  git fetch upstream pull/8142/head
  git checkout FETCH_HEAD

Isn't it more like the following?:

  git clone https://github.com/github/dmca.git
  git fetch origin pull/8142/head
  git checkout FETCH_HEAD

I was just modifying the parent comment, which assumes an existing repository.

Since we’re fiddling with things in this way, if you were just trying to get a copy of the contents, this’ll do that about most efficiently:

  git init
  git fetch --depth=1 https://github.com/github/dmca pull/8142/head
  git checkout FETCH_HEAD

(I don’t think you can git-clone an arbitrary ref, only a branch.)