netbox: workaround to allow composible python packageOverrides

[stuebinm]

the packageOverrides of python unfortunately does not compose. Since netbox's definition uses packageOverrides internally, this means something like netbox.override { python3 = python3.override { packageOverrides { ... }; }; } won't work as expected, since only the package override defined last is applied.

see #44426 for related discussion.

Description of changes

replaces the use of .override with .overrideScope, as suggested in #44426 (comment)

(note: there's an alternative solution which also does the trick:

python3.override (super: { 
 packageOverrides = 
   let ours = self: super: { django = super.django_4; }; 
   in if super ? packageOverrides
    then lib.composeExtensions super.packageOverrides ours
    else ours;
})

I do not know if there are any advantages or disadvantages to either approach, so I've gone with the one suggested in the above-linked comment)

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/)
• 23.05 Release Notes (or backporting 22.11 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.

[RaitoBezarius]

Thank you for this change!