[build] Nix build fails because NodeJS 20 was marked as insecure in nixpkgs

[sgiath]

Nixpkgs marked Node 20 as insecure because it reached end-of-life which makes the build of openspec package fail.

https://github.com/Fission-AI/OpenSpec/blob/main/flake.nix#L58 this line should be updated to use either nodejs_22, nodejs_24 or just simply nodejs

error:
       … while calling the 'head' builtin
         at «github:NixOS/nixpkgs/f83fc3c307e74bc5fd5adb7eb6b8b13ffd2a36e1?narHash=sha256-cCO8aTqss5x9Ky8GWkpY0Hy5fyTZEbtifSUV8QjSzic%3D»/lib/attrsets.nix:1712:13:
         1711|           if length values == 1 || pred here (elemAt values 1) (head values) then
         1712|             head values
             |             ^
         1713|           else

       … while evaluating the attribute 'value'
         at «github:NixOS/nixpkgs/f83fc3c307e74bc5fd5adb7eb6b8b13ffd2a36e1?narHash=sha256-cCO8aTqss5x9Ky8GWkpY0Hy5fyTZEbtifSUV8QjSzic%3D»/lib/modules.nix:1167:7:
         1166|     // {
         1167|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |       ^
         1168|       inherit (res.defsFinal') highestPrio;

       … while evaluating the option `system.build.toplevel':

       … while evaluating definitions from `/nix/store/1hb1glkkpl6vjjpfrwzmvjyvhcyqfxfk-source/nixos/modules/system/activation/top-level.nix':

       … while evaluating the option `warnings':

       … while evaluating definitions from `/nix/store/1hb1glkkpl6vjjpfrwzmvjyvhcyqfxfk-source/nixos/modules/system/boot/systemd.nix':

       … while evaluating the option `systemd.services.home-manager-sgiath.serviceConfig':

       … while evaluating definitions from `/nix/store/h93zbs1bsgn8nf8xldsxdh65w0ji1yi3-source/nixos':

       … while evaluating the option `home-manager.users.sgiath.home.activation.installPackages.data':

       … while evaluating definitions from `/nix/store/h93zbs1bsgn8nf8xldsxdh65w0ji1yi3-source/modules/home-environment.nix':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: Refusing to evaluate package 'nodejs-20.20.2' in /nix/store/1hb1glkkpl6vjjpfrwzmvjyvhcyqfxfk-source/pkgs/development/web/nodejs/nodejs.nix:689 because it is marked as insecure

       Known issues:
        - This NodeJS release has reached its end of life. See https://nodejs.org/en/about/releases/.

       You can install it anyway by allowing this package, using the
       following methods:

       a) To temporarily allow all insecure packages, you can use an environment
          variable for a single invocation of the nix tools:

            $ export NIXPKGS_ALLOW_INSECURE=1

          Note: When using `nix shell`, `nix build`, `nix develop`, etc with a flake,
                then pass `--impure` in order to allow use of environment variables.

       b) for `nixos-rebuild` you can add ‘nodejs-20.20.2’ to
          `nixpkgs.config.permittedInsecurePackages` in the configuration.nix,
          like so:

            {
              nixpkgs.config.permittedInsecurePackages = [
                "nodejs-20.20.2"
              ];
            }

       c) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
          ‘nodejs-20.20.2’ to `permittedInsecurePackages` in
          ~/.config/nixpkgs/config.nix, like so:

            {
              permittedInsecurePackages = [
                "nodejs-20.20.2"
              ];
            }