actions update

.forgejo/workflows/demo.yaml

@@ -6,6 +6,10 @@ jobs:
       - name: checkout
         uses: actions/checkout@v3
 
+      - run: | 
+          apt update
+          apt install python3
+
       - uses: https://github.com/cachix/install-nix-action@v27
         with:
           nix_path: nixpkgs=channel:nixos-unstable