Avoid potential loop_var shadowing (#11162)

With CentOS, kubespray currently produces the following warning:

[WARNING]: TASK: bootstrap-os : Enable Oracle Linux repo: The loop variable
'item' is already in use. You should set the `loop_var` value in the
`loop_control` option for the task to something else to avoid variable
collisions and unexpected behavior.

This could bites us in nasty ways, so fix it.

roles/bootstrap-os/tasks/main.yml

@@ -24,10 +24,12 @@
       - vars/
       skip: True
   - name: Include tasks
-    include_tasks: "{{ item }}"
+    include_tasks: "{{ included_tasks_file }}"
     with_first_found:
     - <<: *search
       paths: []
+    loop_control:
+      loop_var: included_tasks_file
 
 
 - name: Create remote_tmp for it is used by another module