[ansible] Checking for multiple conditions using "when" on single task in ansible

Also you can use default() filter. Or just a shortcut d()

- name: Generating a new SSH key for the current user it's not exists already
  local_action:
    module: user
    name: "{{ login_user.stdout }}"
    generate_ssh_key: yes 
    ssh_key_bits: 2048
  when: 
    - sshkey_result.rc == 1
    - github_username | d('none') | lower == 'none'