Remove `isShallow` check on root source
This seems to fix #74, by still using fetchGit even when the git repo is shallow.
I suspect this means issues similar to #74 can still occur when the flake is not a git repo, perhaps due to an underlying issue with "${src}" not correctly copying to store in some scenarios when nix-instantiate --eval is used?
Bumping for feedback 🙃
Another friendly bump
CC @roberth for review.
Seems reasonable, and I like that this is a simplification.
isShallow and its usage were introduced in https://github.com/NixOS/flake-compat/commit/2c2a50af4dd77d8457284301b521448289b5a3ed without explanation why isShallow would have been a prerequisite for validity.
Shallow repos should work just fine.