add nixpkgs

Author: nohzafk

.github/workflows/schedule.yaml

@@ -11,7 +11,9 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Set up Nix
-        uses: cachix/install-nix-action@v22
+        uses: cachix/install-nix-action@v27
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
 
       - name: Install just
         run: |