E.g. `pkgs.bundlerEnv { passthru = { ... }; ... }` previously would not
result in the `passthru` attrs not being concatenated onto the returned
derivation. Now it will be.
E.g. `pkgs.bundlerEnv { passthru = { ... }; ... }` previously would not
result in the `passthru` attrs not being concatenated onto the returned
derivation. Now it will be.