Motivation for this change

This test is sometimes flaky on hydra as at the time of the git clone
the network isn't really configured yet[1]. That problem doesn't seem to
occur locally but if you run it on a machine with high enough load (such
as hydra build machines). Hopefully this will make the test not flaky
anymore.

[1] https://hydra.nixos.org/build/118710378/nixlog/21/raw

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/)