Handle matrix_playbook_reverse_proxy_type being "none" when deciding on Coturn certificate parameters

group_vars/matrix_servers

@@ -1919,6 +1919,7 @@ matrix_coturn_tls_cert_path: |-
     {
       'nginx-proxy': '/fullchain.pem',
       'traefik': '/certificate.crt',
+      'none': '',
     }[matrix_playbook_reverse_proxy_type]
   }}
 
@@ -1927,6 +1928,7 @@ matrix_coturn_tls_key_path: |-
     {
       'nginx-proxy': '/privkey.pem',
       'traefik': '/privatekey.key',
+      'none': '',
     }[matrix_playbook_reverse_proxy_type]
   }}