pythonPackages.tldextract: add missing setuptools_scm dependency

[emmanuelrosa]

Motivation for this change

This change adds setuptools_scm as a dependency so that tldextract builds.

The build was failing because it was trying to dowload (presumably setuptools-scm) during the buildPhase, which of course is not allowed. Adding it as a dependency resolved the issue.

tldextract is a dependency of qutebrowser, which is working with this change.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.