[stable31] chore(deps): Update flake to NixOS 26.05

[backportbot]

Backport of PR #60896

[provokateurin]

       error: Refusing to evaluate package 'nodejs-20.20.2' in /nix/store/i936ws2xplkqgbzkxkacqqq2dpag3ndf-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"
              ];
            }