"error: path '/nix/var/nix/profiles/per-user/root/channels/nixpkgs' is a symlink" in 2.20.0

[l0b0]

Describe the bug

83c067c broke my NixOS build:

       … while evaluating attribute 'installPhase' of derivation 'security-wrapper-VBoxHeadless-x86_64-unknown-linux-musl'
         at /nix/var/nix/profiles/per-user/root/channels/nixpkgs/nixos/modules/security/wrappers/wrapper.nix:16:3:
       error: path '/nix/var/nix/profiles/per-user/root/channels/nixpkgs' is a symlink

This is happening both on nixos-unstable and nixos-23.11.

Steps To Reproduce

1. Run the pipeline

Expected behavior

At this level, Nix should behave the same as the previous 20+ versions.

nix-env --version output

nix-env (Nix) 2.20.0 (assumed based on the diff)

Additional context

Add any other context about the problem here.

Priorities

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