Add missing translation string

    * custom_components/daikin_onecta/strings.json:

Author: jwillemsen

custom_components/daikin_onecta/strings.json

@@ -20,7 +20,8 @@
       "authorize_url_timeout": "[%key:common::config_flow::abort::oauth2_authorize_url_timeout%]",
       "no_url_available": "[%key:common::config_flow::abort::oauth2_no_url_available%]",
       "user_rejected_authorize": "[%key:common::config_flow::abort::oauth2_user_rejected_authorize%]",
-      "reauth_successful": "[%key:common::config_flow::abort::reauth_successful%]"
+      "reauth_successful": "[%key:common::config_flow::abort::reauth_successful%]",
+      "single_instance_allowed": "[%key:common::config_flow::abort::single_instance_allowed%]",
     },
     "create_entry": {
       "default": "[%key:common::config_flow::create_entry::authenticated%]"