Revert "Revert "initialized git repo should use the set http_proxy""

This reverts commit f8a833cfb1.
This makes sure the check returns a zero code.

See discussion on https://github.com/NixOS/nixpkgs/commit/5af576f

pkgs/build-support/fetchgit/nix-prefetch-git

@@ -83,6 +83,7 @@ init_remote(){
     local url=$1
     git init
     git remote add origin $url
+    [ -n "$http_proxy" ] && git config http.proxy $http_proxy || true
 }
 
 # Return the reference of an hash if it exists on the remote repository.