The new tarballBuilder fails when HOME variable set on execution host

[terlar]

Bug description

I discovered on my CI that sets a HOME variable that the tarballBuilder fails with:

error: opening '/github/home/.nix-channels' for writing: No such file or directory
Error: Process completed with exit code 1.

This is because my GitHub Runner has set this HOME variable.

To Reproduce

Steps to reproduce the behavior:

sudo HOME=/home/unknown nix run --print-build-logs github:nix-community/NixOS-WSL#nixosConfigurations.modern.config.system.build.tarballBuilder

Expected behavior
Successful build of tarballBuilder.

Logs

Include relevant console logs

error: opening '/github/home/.nix-channels' for writing: No such file or directory
Error: Process completed with exit code 1.

[terlar]

This could be fixed like this:

diff --git a/modules/build-tarball.nix b/modules/build-tarball.nix
index 3d787ab..a53ac1a 100644
--- a/modules/build-tarball.nix
+++ b/modules/build-tarball.nix
@@ -76,7 +76,7 @@ in
           --substituters ""

         echo "[NixOS-WSL] Adding channel..."
-        nixos-enter --root "$root" --command 'nix-channel --add https://github.com/nix-community/NixOS-WSL/archive/refs/heads/main.tar.gz nixos-wsl'
+        nixos-enter --root "$root" --command 'HOME=/root nix-channel --add https://github.com/nix-community/NixOS-WSL/archive/refs/heads/main.tar.gz nixos-wsl'

         echo "[NixOS-WSL] Adding default config..."
         ${if cfg.configPath == null then ''