update-python-libraries: Add support for fetchgit

Previously when packages that required the git fetcher were updated, we
would wrongly rely on `nix-prefetch-url`, which would reliable break the
hash.

Instead we need to use `nix-prefetch-git` to determine the proper hash,
when the relevant attributes are present.

pkgs/development/interpreters/python/update-python-libraries/default.nix

@@ -1,8 +1,9 @@
-{ python3, runCommand, git, nix }:
+{ python3, runCommand, git, nix, nix-prefetch-git }:
 
 runCommand "update-python-libraries" {
   buildInputs = [
     nix
+    nix-prefetch-git
     (python3.withPackages(ps: with ps; [ packaging requests toolz ]))
     git
   ];