qt6.qtbase: fix package reference in setup hook

[mjoerg]

After ceec85b, @out@ incorrectly referenced the setup hook instead of the actual package.

fixes #493843

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

[SFrijters]

Seems I was going in the same direction with my fix, but with a slightly different implementation: #493988 . I prefer that one because your solution moves away from the compatibility with __structuredAttrs and reliance on substituteAll that the original PR was trying to accomplish.

makeSetupHook needs some work (e.g. it explicitly sets __structuredAttrs = false;), so my fix is also a workaround for now, hopefully things can be set up to work more ergonomically later.