darwin-rebuild should use `sudo -H` instead of `sudo` to work around Nix warning

[lilyball]

Nix 2.10 has started printing a warning whenever the current user doesn't own $HOME, which is the case on macOS when running sudo nix because macOS sudo doesn't reset $HOME by default. darwin-rebuild is currently running sudo nix-env -p "$profile" --set "$systemConfig". This command shouldn't care about $HOME[^1] and yet it now triggers a warning. It would be nice to avoid the warning.

[^1]: In theory $HOME can affect it through per-user nix.conf files but that seems rather niche.