icu73: use buildPackages.icu73 for nativeBuildRoot

[afh]

Description of changes

I might be missing something, yet it seems the icu73 package definition in all-packages.nix may have a typo as it uses buildPackages.icu72 instead of buildPackages.icu73 as its nativeBuildRoot.

ℹ️ This PR should possibly be closed in favour of #289814 if that PR is headed in the right direction.

Do let me know if this is an actual issue and if yes, whether staging is the correct merge base for this PR.

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/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 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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[afh]

ℹ️ icu73, icu73.passthru.tests on x86_64-darwin failed due to: error: building of '/nix/store/a8fnjl2ak7c87j8scxjnj5yj62z7a8qn-llvm-16.0.6.drv^dev' from .drv file timed out after 3600 seconds

[afh]

Closing as this PR is obsoleted by merged #290266.