update nixpkgs to unstable

nixpkgs on previously 22.05 changed something in regard to
`python.interpreter`. Updating to a version atleast as recent as used in
other runtime verification repositories fixes this.

Author: juliankuners

{{cookiecutter.project_slug}}/flake.nix

@@ -1,7 +1,7 @@
 {
   description = "{{ cookiecutter.project_slug }} - {{ cookiecutter.description }}";
   inputs = {
-    nixpkgs.url = "nixpkgs/nixos-22.05";
+    nixpkgs.url = "nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
     poetry2nix.url = "github:nix-community/poetry2nix";
   };