build: Simplify CI pipeline

Fixed up woodpecker to not use a persistent volume, so now we can have a
more regular and portable config

.woodpecker/ci.yaml

@@ -6,28 +6,6 @@ when:
 
 steps:
   check:
-    image: alpine
-    volumes:
-      - nix:/nix
+    image: docker.io/nixpkgs/nix-flakes:nixos-24.05
     commands:
-      # install nix
-      - |
-        test -f /nix/installer || wget -O /nix/installer https://github.com/DeterminateSystems/nix-installer/releases/download/v0.18.0/nix-installer-x86_64-linux
-        chmod +x /nix/installer
-        rm -f /nix/receipt.json /nix/nix-installer
-        /nix/installer install linux --init=none --no-confirm
-        . /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh
-
-      # configure nix
-      - |
-        mkdir -p /etc/nix
-        cat <<EOF > /etc/nix/nix.conf
-        sandbox = false
-        experimental-features = nix-command flakes
-        EOF
-
-      # build
-      - nix build .#patos_image
-
-      # check
       - nix flake check