fix typo in bgp neighbor template

geant/gap_ansible/roles/promote_p_to_pe/templates/routers/nokia/router/bgp_neighbor.j2

@@ -4,7 +4,7 @@
                     <description>{{ neighbor.description }}</description>
                     <group>{{ neighbor.group }}</group>
                   {% if neighbor.auth_key is defined %}
-                    <authentication-key>{{ neighbor.auth_key }</authentication-key>
+                    <authentication-key>{{ neighbor.auth_key }}</authentication-key>
                   {% endif %}
                   {% if neighbor.hold_time is defined %}
                     <hold-time>