This does not include any automation for the release branch, but
is based on the configuration of https://github.com/NixOS/nix/pull/12349
pre-commit run -a nixfmt-rfc-style
Add several tests for git fetching:
- shallow-cache-separation: can fetch the same repo shallowly and non-shallowly
- shallow-ignore-ref: ensure that ref gets ignored when shallow=true is set
- ssh-shallow: can fetch a git repo via ssh using shallow=1
