Sending headers for legacy ws client in graphiql subscriptions

I am using legacy WS client for the Graphiql subscriptions. my code looks as below

```
return createGraphiQLFetcher({
headers,
url: URLs.https
legacyWsClient: new SubscriptionClient(URLs.wss + '?access_token=' + accessTokenProvider(),
{
reconnect: false,
lazy: false,
}),
});
```

I am adding custom headers from the GraphiQL UI and getting added to the HTTP based queries and mutation requests as expected. But custom headers not set in the HTTP upgrade request for subscriptions.