fix flaky condition in education dropdown.

common/test/acceptance/tests/lms/test_account_settings.py

@@ -231,7 +231,8 @@ class AccountSettingsPageTest(AccountSettingsTestMixin, WebAppTest):
 
         for new_value in new_values:
             self.assertEqual(self.account_settings_page.value_for_dropdown_field(field_id, new_value), new_value)
-            self.account_settings_page.wait_for_message(field_id, success_message)
+            # An XHR request is made when changing the field
+            self.account_settings_page.wait_for_ajax()
             if reloads_on_save:
                 self.account_settings_page.wait_for_loading_indicator()
             else: