Motivation for this change

This commit removes a string expansion to check array inclusion in favor of an array traversal.
It uses a named reference since that is perceived to be the code's intent.
(this removes an eval as a positive side effect).

Note that this change comes from a problematic commit and it was proposed in a previous PR.

@aszlig thank you for reviewing this the first time!
I believe that even though the resulting code is slightly different, the semantic meaning should be preserved. I do want to try a hydra test to make sure of my hypothesis.

https://github.com/NixOS/nixpkgs/pull/129903/files

The original commit with some comments bf99a81

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• 21.11 Release Notes (or backporting 21.05 Relase notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.