Typescript RemoteObject does not allow assignment of non-promise value

The following code does not appear to compile using `comlink@4.3.0`
```typescript
type RA = Remote<{foo:string}>
declare const a: RA
a.foo = "bar"
```
On account of `a.foo` being a `Promise` and `"bar"` being a `string`. I understand there's currently [no way to allow separate setter and getter types](https://github.com/microsoft/TypeScript/issues/2521), but it seemed like the code worked differently before moving to `4.3.0`?