Use already_configured_service in NWS strings (#41062)

homeassistant/components/nws/strings.json

@@ -17,7 +17,7 @@
       "unknown": "[%key:common::config_flow::error::unknown%]"
     },
     "abort": {
-      "already_configured": "[%key:common::config_flow::abort::single_instance_allowed%]"
+      "already_configured": "[%key:common::config_flow::abort::already_configured_service%]"
     }
   }
 }