Add all hosts from ansible inventory to ssh known_hosts file of current user

add-to-ssh-known-hosts.yml

- name: Gather facts from 'all' hosts in inventory
  hosts: all
  vars:
    ansible_host_key_checking: false
    ansible_ssh_extra_args: '-o UserKnownHostsFile=/dev/null'
  tasks:
    - setup:
        gather_subset: network

- name: Add public keys to known_hosts file
  hosts: localhost
  connection: local
  vars:
    ssh_known_hosts_file: "{{ lookup('env','HOME') + '/.ssh/known_hosts' }}"
    ssh_known_hosts: "{{ groups['all'] }}"
  tasks:
    - known_hosts:
        path: "{{ ssh_known_hosts_file }}"
        name: "{{ item }}"
        key: "{{ lookup('pipe','ssh-keyscan -T 10 ' + item + ',' + lookup('dig',item)) }}"
        state: present
      loop: "{{ ssh_known_hosts | map('extract', hostvars, ['ansible_fqdn']) | list }}"
      become: no

This is what I needed to get it to work

---
- name: Gather facts from 'all' hosts in inventory
  hosts: all
  vars:
    ansible_host_key_checking: false
    ansible_ssh_extra_args: '-o UserKnownHostsFile=/dev/null'
  tasks:
    - name: Get network info
      ansible.builtin.setup:
        gather_subset: network

- name: Add public keys to known_hosts file
  hosts: localhost
  connection: local
  vars:
    ssh_known_hosts_file: "{{ lookup('env','HOME') + '/.ssh/known_hosts' }}"
    ssh_known_hosts: "{{ groups['all'] }}"
  tasks:
    - name: Add to known_hosts
      ansible.builtin.known_hosts:
        path: '{{ ssh_known_hosts_file }}'
        name: '{{ item }}'
        key: "{{ lookup('pipe', 'ssh-keyscan -T 10 ' + item + ',' + lookup('dig', item)) }}"
        state: present
      with_items: '{{ ssh_known_hosts }}'
      become: false