$ git -c fetch.prune=false fetch --force https://github.com/NixOS/nixpkgs release-20.03:refs/nixpkgs-review/0 pull/97564/head:refs/nixpkgs-review/1
remote: Enumerating objects: 4212, done.
remote: Counting objects: 100% (4212/4212), done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 12000 (delta 4207), reused 4210 (delta 4207), pack-reused 7788
Receiving objects: 100% (12000/12000), 3.62 MiB | 7.22 MiB/s, done.
Resolving deltas: 100% (8631/8631), completed with 1088 local objects.
From https://github.com/NixOS/nixpkgs

• [new branch] release-20.03 -> refs/nixpkgs-review/0
• [new ref] refs/pull/97564/head -> refs/nixpkgs-review/1
• [new tag] 20.03 -> 20.03
  $ git worktree add /home/danielle/.cache/nixpkgs-review/pr-97564/nixpkgs 8658d6c
  Preparing worktree (detached HEAD 8658d6c)
  Updating files: 100% (21037/21037), done.
  HEAD is now at 8658d6c Merge pull request [20.03] flashplayer: 32.0.0.330 -> 32.0.0.433 #97538 from taku0/flashplayer-32.0.0.433_20.03
  $ nix-env -f /home/danielle/.cache/nixpkgs-review/pr-97564/nixpkgs -qaP --xml --out-path --show-trace
  $ git merge --no-commit 2227ca3
  Updating 8658d6c..2227ca3
  Fast-forward
  pkgs/servers/traefik/default.nix | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)
  $ nix-env -f /home/danielle/.cache/nixpkgs-review/pr-97564/nixpkgs -qaP --xml --out-path --show-trace --meta
  1 package updated:
  traefik (1.7.21 → 1.7.26)

$ nix build --no-link --keep-going --option build-use-sandbox relaxed -f /home/danielle/.cache/nixpkgs-review/pr-97564/build.nix
[4 built, 62 copied (660.0 MiB), 160.3 MiB DL]
#97564
1 package built:
traefik

[0.0 MiB DL]
$ nix-shell /home/danielle/.cache/nixpkgs-review/pr-97564/shell.nix

[(nxs: nixpkgs-review) pr-97564] $ ./results/traefik/bin/traefik version
Version: 1.7.26