nix: bump nixpkgs; follow nixos-unstable

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I8ba24ece650300380001797216cb44476a6a6964

Author: NotAShelf

flake.lock

@@ -122,7 +122,7 @@
     systems.url = "github:nix-systems/default";
 
     ## Basic Inputs
-    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
 
     flake-parts = {
       url = "github:hercules-ci/flake-parts";