update build.yml,use newest nix version

Author: wrjade

.github/workflows/build.yml

@@ -35,6 +35,7 @@ jobs:
       uses: cachix/install-nix-action@v22
       with:
         nix_path: nixpkgs=channel:nixos-unstable
+        nix_version: "3.8.5"
         extra_nix_config: |
           experimental-features = nix-command flakes
           allow-import-from-derivation = true