tests.nixpkgs-check-by-name: Fix for aliases to packages in pkgs/by-name and better testing

[infinisil]

Context

In #275539 I made an oversight which shows itself when you run the tool on the current Nixpkgs:

❯ nix-build -A tests.nixpkgs-check-by-name
/nix/store/k7wwnxbrb2r05g5pw7hxw71gg1gls1dr-nixpkgs-check-by-name
❯ result/bin/nixpkgs-check-by-name --base . .
pkgs.NSPlist: This attribute is defined using `_internalCallByNamePackageFile`, which is an internal function not intended for manual use.
[...]
pkgs.uclibc: This attribute is defined using `_internalCallByNamePackageFile`, which is an internal function not intended for manual use.
pkgs.win-virtio: This attribute is defined using `_internalCallByNamePackageFile`, which is an internal function not intended for manual use.
Validation failed, see above errors

See #281374 to prevent the broken tooling from being used on master, that should be merged fairly soon before the nixos-unstable channel updates in like a day.

The problem

The problem is that there's some detection logic that makes sure the internal _internalCallByNamePackageFile attribute isn't used by packages.

If such a top-level attribute that's not in pkgs/by-name was detected to use this, an error is thrown. However, the detection logic can't distinguish between aliases and non-aliases.

So it gives errors even for aliases to packages defined in pkgs/by-name, e.g.

nixpkgs/pkgs/top-level/aliases.nix

Line 1099 in 5df0c94

win-virtio = virtio-win; # Added 2023-10-17

https://github.com/NixOS/nixpkgs/blob/5df0c94c5ed9c4b9664d63047f2f3a7f93c0bb43/pkgs/top-level/all-packages.nix#L28854

The solution

It would be non-trivial to improve the detection logic, so instead this PR just changes the tool to not give an error in these cases.

Furthermore, a passthru.tests is added, addressing #256789 and preventing future such problems. It should be triggered automatically after ofborg finishes evaluation of a PR with a tests.nixpkgs-check-by-name: ... commit.

---

Add a 👍 reaction to pull requests you find important.

[infinisil]

@ofborg build tests.nixpkgs-check-by-name tests.nixpkgs-check-by-name.tests

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/ci-will-soon-enforce-pkgs-by-name-for-new-packages/38098/2

[philiptaron]

Sad but makes sense.

[quantenzitrone]

all changes are trivial enough for me to understand
so LGTM