Use new cmd for nix builds

.drone.yml

@@ -27,8 +27,16 @@ steps:
   volumes:
     - name: deps
       path: /nix/store
+  environment:
+    DRONE_SSH_KEY:
+      from_secret: DRONE_SSH_KEY
+    GIT_C3C_KNOW_HOSTS:
+      from_secret: GIT_C3C_KNOW_HOSTS
   commands:
-    - nix-build --argstr version ${DRONE_TAG} --argstr rev ${DRONE_COMMIT} .#image
+    - mkdir /root/.ssh
+    - echo "$DRONE_SSH_KEY" > /root/.ssh/id_ed25519
+    - echo "$GIT_C3C_KNOW_HOSTS" > /root/.ssh/known_hosts
+    - nix --extra-experimental-features nix-command --extra-experimental-features flakes build .#image
 
 - name: publish
   image: docker:dind
@@ -87,6 +95,6 @@ services:
 
 ---
 kind: signature
-hmac: df9a2fb07428f545bc41b36d4c8b53e0e7223333f614e2d5d890a1adbd7f324b
+hmac: df39c218d4fba826757d713ce80db6debfed40c0b49215cfdf871dc37046f558
 
 ...