[stable/2023.1 only] Fix missing test fix for ext gw

A fix for an invalid cherry pick [0] missed updating all
the unit tests that had an invalid key. Fix it.

[0] https://review.opendev.org/c/openstack/neutron/+/913408/

Related-bug: #2057942
Change-Id: I167067c185b63e7e1b4b3c0821e73315c60ea018

Author: brianphaley

neutron/tests/unit/plugins/ml2/drivers/ovn/mech_driver/ovsdb/test_maintenance.py

@@ -979,7 +979,7 @@ def test_add_gw_port_info_to_logical_router_port_no_action_needed(self):
         internal_net_id = uuidutils.generate_uuid()
         routers_db = [{
             'id': uuidutils.generate_uuid(),
-            'external_gateways': [{'network_id': ext_net_id}]}]
+            'external_gateway_info': {'network_id': ext_net_id}}]
         ext_gw_lrp = fakes.FakeOvsdbRow.create_one_ovsdb_row(
             attrs={'external_ids': {
                 constants.OVN_NETWORK_NAME_EXT_ID_KEY: