Ansible include task only if file exists

The with_first_found conditional can accomplish this without a stat or local_action. This conditional will go through a list of local files and execute the task with item set to the path of the first file that exists.
Including skip: true on the with_first_found options will prevent it from failing if the file does not exist.

Example:

- hosts: localhost
  connection: local
  gather_facts: false

  tasks:
    - include: "{{ item }}"
      with_first_found:
        - files:
            - /home/user/optional/file.yml
          skip: true