k8s/preinstall: Turn AND condition into a list

roles/kubernetes/preinstall/tasks/pre_upgrade.yml

@@ -20,4 +20,6 @@
     creates: "{{ inventory_dir }}/credentials"
   delegate_to: localhost
   become: no
-  when: old_credential_dir.stat.exists and not new_credential_dir.stat.exists
+  when:
+    - old_credential_dir.stat.exists
+    - not new_credential_dir.stat.exists