Fixup one more missing kubespray-defaults (#7375)

"The error was: 'proxy_disable_env' is undefined\n\nThe error appears to
be in '<censored>scale.yml': line 72, column 7"

Fixes 067db686

Signed-off-by: Etienne Champetier <e.champetier@ateme.com>

scale.yml

@@ -68,6 +68,8 @@
   environment: "{{ proxy_disable_env }}"
   gather_facts: False
   tags: kubeadm
+  roles:
+    - { role: kubespray-defaults }
   tasks:
     - name: include needed vars
       include_vars: roles/kubespray-defaults/defaults/main.yaml