Update signal-desktop to unstable

This fixes linking of new devices.

configuration.nix

@@ -4,6 +4,12 @@
 
 { config, lib, pkgs, ... }:
 
+let unstable = import (builtins.fetchTarball {
+  name = "nixos-unstable-2024-12-08";
+  url = "https://github.com/NixOS/nixpkgs/archive/868be2c9df2ffdb40b6aee3d156f1df603555539.tar.gz";
+  sha256 = "0s7xzhv4a98j6kbas1q4pd3ln1l5hfamp4db4wx5mif0110n5scv";
+}) {};
+in
 {
   nix.settings.experimental-features = [ "nix-command" "flakes" ];
   imports =
@@ -135,7 +141,7 @@
     neovim
     docker-compose
     nodejs
-    signal-desktop
+    unstable.signal-desktop
     telegram-desktop
     rustup gcc pkg-config
     gimp