Make sops-nix follows the correct nixpkgs channels

Signed-off-by: Benoit Donneaux <benoit@leastauthority.com>

Author: btlogy

flake.nix

@@ -13,8 +13,8 @@
     sops-nix = {
       url = "github:Mic92/sops-nix";
       # Flip those when the last systems can start using this module
-      inputs.nixpkgs.follows = "nixpkgs";
-      inputs.nixpkgs-stable.follows = "nixpkgs-oldstable";
+      inputs.nixpkgs.follows = "nixpkgs-unstable";
+      inputs.nixpkgs-stable.follows = "nixpkgs";
     };
     simple-nixos-mailserver = {
       url = "gitlab:simple-nixos-mailserver/nixos-mailserver/nixos-24.05";