pypy3: fix sitecustomize

[999eagle]

Description of changes

This is a stop-gap solution for pypy3.withPackages to actually find the correct site-packages directory. This should be a workaround for #39356.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 23.11 Release Notes (or backporting 23.05 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.

[FRidh]

#217558 did not fix the issue entirely?

[SuperSandro2000]

When we upgraded past this version and added Python 3.8 support 1, the sitePackages value was never updated, leading bootstrapped-pip to fail to build, because wheel was trying to be located in $out/site-packages, when it was actually installed to $out/lib/pypy3.8/site-packages.

It went into a different direction and now is searching for $out/lib/pypy3.8/lib/pypy3.8/site-packages

[SuperSandro2000]

drafting because of the proper fix in #240301

[SuperSandro2000]

Fixed in #442224