Use of reference strings in meteo france config flow (#40939)

homeassistant/components/meteo_france/strings.json

@@ -21,7 +21,7 @@
     },
     "abort": {
       "already_configured": "City already configured",
-      "unknown": "Unknown error: please retry later"
+      "unknown": "[%key:common::config_flow::error::unknown%]"
     }
   },
   "options": {
@@ -33,4 +33,4 @@
       }
     }
   }
-}
+}