roles: Fix ansible-lint warning on var-naming.

ansible-lint warns if set_fact sets a variable where the name is used
or can be as a parameter for the role.

roles/ipabackup/tasks/copy_backup_from_server.yml

@@ -9,7 +9,7 @@
 
 - name: Set controller destination directory
   ansible.builtin.set_fact:
-    ipabackup_controller_dir:
+    __derived_controller_dir:
         "{{ ipabackup_controller_path | default(lookup('env', 'PWD')) }}/{{
          ipabackup_name_prefix | default(ansible_facts['fqdn']) }}_{{
          ipabackup_item }}/"
@@ -35,13 +35,13 @@
   ansible.builtin.fetch:
     flat: yes
     src: "{{ ipabackup_dir }}/{{ ipabackup_item }}/{{ item }}"
-    dest: "{{ ipabackup_controller_dir }}"
+    dest: "{{ __derived_controller_dir }}"
   with_items:
   - "{{ result_find_backup_files.stdout_lines }}"
 
 - name: Fix file modes for backup on controller
   ansible.builtin.file:
-    dest: "{{ ipabackup_controller_dir }}"
+    dest: "{{ __derived_controller_dir }}"
     mode: u=rwX,go=
     recurse: yes
   delegate_to: localhost