hosts: homes: cloudtop: disable 'git' package

A recent update modified `ssh_config`, and nixpkgs' version of OpenSSH
does not know how to deal with those options.

The `git` package does not make use of the system-provided SSH client,
and errors-out.

Given that those patches are never going to be upstreamed, just override
the `git` package, and use the system-provided one instead...

hosts/homes/ambroisie@ambroisie/default.nix

@@ -1,5 +1,5 @@
 # Google Cloudtop configuration
-{ ... }:
+{ lib, pkgs, ... }:
 {
   # Google specific configuration
   home.homeDirectory = "/usr/local/google/home/ambroisie";
@@ -12,4 +12,6 @@
   systemd.user.sessionVariables = {
     LD_PRELOAD = "/lib/x86_64-linux-gnu/libnss_cache.so.2\${LD_PRELOAD:+:}$LD_PRELOAD";
   };
+
+  programs.git.package = lib.mkForce pkgs.emptyDirectory;
 }