Relay 10: difficulty with optimistic response and @raw_response_type

Hi, we have an issue with an optimistic response when using the new Relay 10. This is our mutation:

```graphql
mutation SidebarLayoutMarkAsSeenMutation($leadID: ID!) @raw_response_type {
updateLead(input: { id: $leadID, wasSeen: true }) {
... on Lead {
wasSeen
}
}
}
```

And here is how we do the optimistic response:

```js
markAsSeen({
variables: { leadID },
optimisticResponse: {
updateLead: {
__typename: 'Lead',
// __isNode: 'Lead', <<< should this be here or not?
id: leadID,
wasSeen: true,
},
},
});
```

This works fine with Relay 9, however, Relay 10 generates different Flow (or in our case TS) types which forces us to write also `__isNode` into the optimistic response. That's however also not okay because Relay complains with the following error:

```text
Warning: Expected `optimisticResponse` to match structure of server response for mutation `SidebarLayoutMarkAsSeenMutation`, please remove all fields of
{
"updateLead": {
"__isNode": {}
}
}
```

Here are the generated types for Flow:

```js
export type SidebarLayoutMarkAsSeenMutationRawResponse = {|
+updateLead: ?({|
+__typename: "Lead",
+__isNode: "Lead",
+id: string,
+wasSeen: ?boolean,
|} | {|
+__typename: string,
+__isNode: string,
+id: string,
|})
|};
```

Or for TypeScript which looks fairly similar so I don't think that's the problem:

```typescript
export type SidebarLayoutMarkAsSeenMutationRawResponse = {
readonly updateLead: ({
readonly __typename: "Lead";
readonly __isNode: "Lead";
readonly id: string;
readonly wasSeen: boolean | null;
} | {
readonly __typename: string;
readonly __isNode: string;
readonly id: string;
}) | null;
};
```

My question is: how should we handle this situation? I am not sure what is the right strategy here and what does `__isNode` exactly mean in this case. 🤔

Thank you very much for having a look!