chore: use new nixpkgs with overlay which bring back go_1_20 instead of using old nixpkgs (#1162)

flake.nix

@@ -1,8 +1,8 @@
 {
   description = "基于 ZeroBot 的 OneBot 插件";
 
-  # pin nixpkgs to preserve dropped go_1_20
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/33c51330782cb486764eb598d5907b43dc87b4c2";
+  inputs.nixpkgs-with-go_1_20.url = "github:NixOS/nixpkgs/33c51330782cb486764eb598d5907b43dc87b4c2";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   inputs.flake-utils.url = "github:numtide/flake-utils";
   inputs.gomod2nix.url = "github:nix-community/gomod2nix";
   inputs.gomod2nix.inputs.nixpkgs.follows = "nixpkgs";
@@ -11,14 +11,25 @@
   outputs = {
     self,
     nixpkgs,
+    nixpkgs-with-go_1_20,
     flake-utils,
     gomod2nix,
-  }: let
+    ...
+  } @ inputs: let
     allSystems = flake-utils.lib.allSystems;
   in (
     flake-utils.lib.eachSystem allSystems
     (system: let
-      pkgs = nixpkgs.legacyPackages.${system};
+      old-nixpkgs = nixpkgs-with-go_1_20.legacyPackages.${system};
+      pkgs = import nixpkgs {
+        inherit system;
+
+        overlays = [
+          (_: _: {
+            go_1_20 = old-nixpkgs.go_1_20;
+          })
+        ];
+      };
 
       # The current default sdk for macOS fails to compile go projects, so we use a newer one for now.
       # This has no effect on other platforms.
@@ -26,11 +37,10 @@
     in {
       # doCheck will fail at write files
       packages = rec {
-
-        ZeroBot-Plugin =
-          (callPackage ./. {
+        ZeroBot-Plugin = (callPackage ./. (inputs
+          // {
             inherit (gomod2nix.legacyPackages.${system}) buildGoApplication;
-          })
+          }))
           .overrideAttrs (_: {doCheck = false;});
 
         default = ZeroBot-Plugin;
@@ -43,7 +53,6 @@
             pkgs.cacert
           ];
         };
-
       };
       devShells.default = callPackage ./shell.nix {
         inherit (gomod2nix.legacyPackages.${system}) mkGoEnv gomod2nix;