add nixpkgs to NIX_PATH for release

Author: expipiplus1

.github/workflows/release.yml

@@ -12,6 +12,7 @@ jobs:
     steps:
     - uses: cachix/install-nix-action@v12
       with:
+        nix_path: nixpkgs=channel:nixos-unstable
         extra_nix_config: |
           trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= orion:s0C06f1M46DCpHUUP2r8iIrhfytkCbXWltMeMMa4jbw= expipiplus1/update-nix-fetchgit:Z33K0KEImsos+kVTFvZxfLxaBi+D1jEeB6cX0uCo7B0=
           substituters = https://cache.nixos.org/ s3://nix-cache?region=ap-southeast-1&scheme=https&endpoint=binarycache.home.monoid.al