Ruru headers are not passed along with requests to `/graphql/stream`
### Summary

Now that https://github.com/graphile/crystal/issues/1828 is fixed, the next request that Ruru does is to the `/graphql/stream` endpoint. However, it also doesn't send the headers along with the request, so it receives a 403 from our backend and causes Ruru to crash to a white screen with the following in the console:

```
GET http://localhost:4180/graphql/stream 403 (Forbidden)
graphiql:24 Ruru: Failed to connect to event stream Event {isTrusted: true, type: 'error', target: EventSource, currentTarget: EventSource, eventPhase: 2, …}
n @ graphiql:24
error (async)
(anonymous) @ graphiql:24
il @ graphiql:24
xu @ graphiql:24
uu @ graphiql:24
zi @ graphiql:24
(anonymous) @ graphiql:24
Eu @ graphiql:24
ou @ graphiql:24
E @ graphiql:24
L @ graphiql:24
graphiql:24 Error: Lifecycle management error for EventSource
    at graphiql:24:1692214
    at il (graphiql:24:700503)
    at xu (graphiql:24:720625)
    at uu (graphiql:24:712926)
    at zi (graphiql:24:653915)
    at graphiql:24:719427
    at Eu (graphiql:24:719432)
    at ou (graphiql:24:711929)
    at E (graphiql:24:745027)
    at MessagePort.L (graphiql:24:745559)
ps @ graphiql:24
n.callback @ graphiql:24
Bo @ graphiql:24
wl @ graphiql:24
Al @ graphiql:24
bl @ graphiql:24
(anonymous) @ graphiql:24
Eu @ graphiql:24
uu @ graphiql:24
zi @ graphiql:24
(anonymous) @ graphiql:24
Eu @ graphiql:24
ou @ graphiql:24
E @ graphiql:24
L @ graphiql:24
graphiql:24 Uncaught Error: Lifecycle management error for EventSource
    at graphiql:24:1692214
    at il (graphiql:24:700503)
    at xu (graphiql:24:720625)
    at uu (graphiql:24:712926)
    at zi (graphiql:24:653915)
    at graphiql:24:719427
    at Eu (graphiql:24:719432)
    at ou (graphiql:24:711929)
    at E (graphiql:24:745027)
    at MessagePort.L (graphiql:24:745559)
(anonymous) @ graphiql:24
il @ graphiql:24
xu @ graphiql:24
uu @ graphiql:24
zi @ graphiql:24
(anonymous) @ graphiql:24
Eu @ graphiql:24
ou @ graphiql:24
E @ graphiql:24
L @ graphiql:24
```

### Steps to reproduce

1. Enter custom headers in the 'Headers' section.
2. Make sure that "Save headers" is ticked.
3. Refresh the Ruru page
4. Check the Network tab, where you can confirm that the POST to `/graphql` for the introspection query does include the custom headers, but the GET to `/graphql/stream` does not.

### Expected results

Headers should be send along with the GET to `/graphql/stream`.

### Actual results

They are not.

### Additional context

Ruru version 2.0.0-beta.10

### Possible Solution

Attach the custom headers to the HTTP call.
