💬 Add non-translated STR_DONE

Marlin/src/core/language.h

 #define STR_SAVED_POS                       "Position saved"
 #define STR_RESTORING_POS                   "Restoring position"
 #define STR_INVALID_POS_SLOT                "Invalid slot. Total: "
+#define STR_DONE                            "Done."
 
 #define STR_SD_CANT_OPEN_SUBDIR             "Cannot open subdir "
 #define STR_SD_INIT_FAIL                    "No SD card"

Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

     settings.load_mesh(param.KLS_storage_slot);
     storage_slot = param.KLS_storage_slot;
 
-    SERIAL_ECHOLNPGM("Done.");
+    SERIAL_ECHOLNPGM(STR_DONE);
   }
 
   //
     settings.store_mesh(param.KLS_storage_slot);
     storage_slot = param.KLS_storage_slot;
 
-    SERIAL_ECHOLNPGM("Done.");
+    SERIAL_ECHOLNPGM(STR_DONE);
   }
 
   if (parser.seen_test('T'))

Marlin/src/gcode/config/M43.cpp

     }
     SERIAL_EOL();
   }
-  SERIAL_ECHOLNPGM("Done.");
+  SERIAL_ECHOLNPGM(STR_DONE);
 
 } // toggle_pins