Skip n8n Deploy stack task in check mode

The command module validates args.chdir before honoring check mode, so
dry runs fail with ENOENT on the stack dir (file task only pretends to
create it). Gate Deploy stack on ansible_check_mode — dry runs should
not run docker compose up anyway.

playbooks/n8n.yml

@@ -99,4 +99,5 @@
     - name: Deploy stack
       command: docker compose up -d
       args:
-        chdir: "{{ stack_dir }}"
+        chdir: "{{ stack_dir }}"
+      when: not ansible_check_mode