Darwin: can't update unstable channel due to case-sensitive issues

[kevingriffin]

Describe the bug

Updating the unstable channel fails on Darwin:

         specified: sha256:04h7r496nc0vvd45d2v1ml1rjgb5hfgmp67sbqz1bz98vyi2r0jb
         got:       sha256:1alxxmr1dzn4vyfzcvgcs12mym0rh5l4vir4x861fiybwhx3b41x

this seems to be due to the by-default case-preserving nature of APFS (and HFS+), introduced with this PR:

#178509

which adds a path tools/x11 which to macOS is the same as the already existing tools/X11 path.

Steps To Reproduce

Steps to reproduce the behavior:

1. Add the unstable channel to a macOS machine
2. nix-channel --update

Expected behavior

A new version of the channel is successfully added to the machine.

Notify maintainers

@azahi

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

 - system: `"aarch64-darwin"`
 - host os: `Darwin 22.0.0, macOS 13.0`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.3.16`
 - channels(kevin): `"darwin, nixpkgs-22.11pre382065.5643714dea5"`
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
 - nixpkgs: `/Users/kevin/.nix-defexpr/channels/nixpkgs`

[azahi]

My bad. Should we add a channel blocker label to this to get the PR merged faster?