Ansible same host unreachable in 2 plays - ansible

Question

I met with a "surprising" error from Ansible.
I have hosts: localhost in 2 consecutive plays.
play1 is ok, in play2 Ansible 2.9 says "localhost" unreachable.
In host_vars/localhost, I have ansible_connection: local
---
############ Play 1 ###############
- name: Test Play 1
hosts: localhost
gather_facts: no
tasks:
- name: Set facts
set_fact:
action_host: localhost
############ Play 2 ###############
- name: Test Play 2
hosts: localhost
gather_facts: no
tasks:
- name: Test Play 2
shell: |
echo toto
Output:
PLAY [Test Play 1] ***********************************************************************************************
TASK [Set facts] *************************************************************************************************
ok: [localhost]
PLAY [Test Play 2] ***********************************************************************************************
TASK [Test Play 2] ***********************************************************************************************
fatal: [localhost]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).", "unreachable": true}
PLAY RECAP *******************************************************************************************************
localhost : ok=1 changed=0 unreachable=1 failed=0 skipped=0 rescued=0 ignored=0
$ cat host_vars/localhost
ansible_connection: local

Answer 1

Thanks for all your answers.
Resolved, finally this was simply because, the playbook was not in the same directory where ansible.cfg was located.
I've copied the file to ~/ansible/.
cd ~/ansible ; ansible-playbook <file>.yaml
Then, All well.
If I simply do:
cp <file>.yaml /tmp/.
ansible-playbook /tmp/<file>.yaml
Then I get the error:
TASK [Gathering Facts] *******************************************************************************************
fatal: [localhost]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).", "unreachable": true}
This is because default connection in /etc/ansible/ansible.cfg is ssh_connection
Thanks all.