MWE for the "Invalid cross-device link" bug

When installing NixOS one may encounter a cryptic "Invalid cross-device link" bug. This is a minimal working example flake for reproducing this bug.

Steps to reproduce

1. Boot a NixOS ISO image in a QEMU VM using BIOS boot and using a VirtIO virtual hard disk. Optionally, set a password using passwd for the nixos user so that the process could be continued over SSH.

2. Enter a Nix shell with Git and with the new Nix command syntax & Flakes enabled:

    NIX_CONFIG='experimental-features = nix-command flakes' nix-shell -p git
   

3. Clone this flake as

    git clone https://github.com/KornelJahn/nixos-crossdev-link-bug-mwe.git
   

4. Enter the repo directory as

    cd nixos-crossdev-link-bug-mwe
   

5. First, try to enter a Nix shell featuring the default package as

    nix shell .#
   

   It should fail with the following ShellCheck error:

   error: builder for '/nix/store/n7mkzq126vljwpvm5cy9kj9skzg8q47w-my-script.drv' failed with exit code 1;
       last 7 log lines:
       >
       > In /nix/store/d585g86virsxax1msalmx5z8wb0mvk81-my-script/bin/my-script line 7:
       > unused=
       > ^----^ SC2034 (warning): unused appears unused. Verify use (or export if used externally).
       >
       > For more information:
       >   https://www.shellcheck.net/wiki/SC2034 -- unused appears unused. Verify use...
       For full logs, run 'nix log /nix/store/n7mkzq126vljwpvm5cy9kj9skzg8q47w-my-script.drv'.
   

   This is what we expect: a meaningful error message.

6. Now try to install NixOS as follows (:warning: THE TARGET VIRTUAL HARD DISK IS WIPED! :warning:):

    ./install.bash
   

   Toward the end of the process, it should also fail, but this time, with a different error message:

   error: filesystem error: cannot rename: Invalid cross-device link [/mnt/nix/store/n7mkzq126vljwpvm5cy9kj9skzg8q47w-my-script.drv.chroot/nix/store/d585g86virsxax1msalmx5z8wb0mvk81-my-script] [/nix/store/d585g86virsxax1msalmx5z8wb0mvk81-my-script]
   

The latter error message is probably caused by the same kernel-related issue as described here. Note that correcting the error in the script inside flake.nix (e.g. by commenting the line unused=) results in a successful installation since ShellCheck won't complain anymore.