add(Duration) or subtract(Duration) in version v1.11.9 is invalid.

```
import dayjs from "dayjs";
import duration from "dayjs/plugin/duration";

dayjs.extend(duration);

let time = dayjs();
const du = dayjs.duration({ milliseconds: 123 });
time = time.add(du);
console.log(time); //<-- Invalid Date !!!!!!!!!
```

`time.add(dayjs.duration({ milliseconds: 123 }))` in version v1.11.9 does not work, and it works normally in version v1.11.8