Render trusted_third_party_id_servers more prettily

roles/matrix-server/templates/synapse/homeserver.yaml.j2

@@ -469,10 +469,10 @@ allow_guest_access: False
 
 # The list of identity servers trusted to verify third party
 # identifiers by this server.
+{% if matrix_synapse_trusted_third_party_id_servers|length > 0 %}
 trusted_third_party_id_servers:
-{% for server in matrix_synapse_trusted_third_party_id_servers %}
-    - {{ server }}
-{% endfor %}
+{{ matrix_synapse_trusted_third_party_id_servers|to_nice_yaml }}
+{% endif %}
 
 # Users who register on this homeserver will automatically be joined
 # to these rooms