Update nixpkgs to 23.05

Author: rszamszur

template/{% if nix %}flake.nix{% endif %}.jinja

@@ -11,7 +11,7 @@
   };
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.11";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
     flake-parts.url = "github:hercules-ci/flake-parts";
     poetry2nix = {
       url = "github:nix-community/poetry2nix?ref=1.42.0";