Update build steps to host instructions

.forgejo/workflows/build-dev.yml

@@ -1,8 +1,3 @@
-on:
-  push:
-    branches:
-      - dev
-
 jobs:
   build:
     runs-on: neils-server-runner
@@ -10,11 +5,5 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v6
 
-      - name: Install Nix
-        uses: https://github.com/cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
-          flake: true
-
       - name: Build
         run: nix build