check-meta: add allowUnfreeLicensePredicate to accept specific unfree licenses

[Pandapip1]

Cherry-picked from #370685

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release 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.

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[Pandapip1]

Bump!

[philiptaron]

I don't find this super compelling in nixpkgs. Isn't this something that ought to land in the code that consumes nixpkgs? allowUnfreePredicate is free to look at the license and run whatever code it desires.

[Pandapip1]

I know that allowUnfreePredicate can do this. This is just a nicer way to configure allowed licenses, IMO.