How do I override some neovim installation dependencies in nix config

Question

Hi I have currently an older version of pynvim in my nixos installation for neovim. This pynvim is configured in nixpkgs-stable. now I want to make use of the one in nixos-unstable since that's a newer version which I need to get a specific neovim pluging working (copilotchat.nvim)

I thought to fix this with an overlay. this is my code for the overlay:

_: pkgs: {
  neovim-unwrapped = pkgs.neovim-unwrapped.overrideAttrs (
    oldAttrs: rec {
      neovim-unwrapped = pkgs.neovim-unwrapped.overrideAttrs {
        extraPython3Packages = [pkgs.unstable.python3Packages.pynvim pkgs.unstable.python3Packages.prompt-toolkit pkgs.unstable.python3Packages.requests];
      };
    }
  );
}

but I still only get the older version of pynvim. if I use pkgs.unstable.neovim-unwrapped in my config I also get the older version of pynvim.

any help?