Stack traces on subgraph fetches are propagated even when `includeStacktraceInErrorResponses` is false
### Issue Description

The `includeStacktraceInErrorResponses` is written to "enrich" errors with stack traces when enabled. But it does not _redact_ stack traces when disabled. If a subgraph includes `extensions.stacktrace` in its response, that will be forwarded to clients.

This is surprising, but relatively easy to fix with a `formatError` hook:

```js
const server = new ApolloServer({
  gateway,
  includeStacktraceInErrorResponses: false,
  formatError: (formatted, original) => {
    // THIS SHOULDN'T BE NECESSARY
    if (formatted.extensions?.stacktrace) {
      delete formatted.extensions.stacktrace;
    }
    return formatted;
  },
});
```

### Link to Reproduction

https://github.com/lennyburdette/curly-succotash/blob/main/gateway.js#L14

### Reproduction Steps

_No response_