[stable-2.20] Fix first_found example (#86224) (#86225)

(cherry picked from commit ce84d31)

Co-authored-by: Matt Clay <matt@mystile.com>

changelogs/fragments/first-found-example.yml

@@ -0,0 +1,2 @@
+bugfixes:
+ - first_found - Correct the "Include tasks only if one of the files exists, otherwise skip" example.

lib/ansible/plugins/lookup/first_found.py

@@ -79,7 +79,7 @@ EXAMPLES = """
 
 - name: Include tasks only if one of the files exists, otherwise skip
   ansible.builtin.include_tasks: '{{ tasks_file }}'
-  when: tasks_file != ""
+  when: tasks_file is not none
   vars:
     tasks_file: "{{ lookup('ansible.builtin.first_found', files=['tasks.yaml', 'other_tasks.yaml'], errors='ignore') }}"