[graphiql] Prettify Query fails

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Current Behavior

"Prettify Query" fails with the following error:

### Expected Behavior

prettify query formats the query (and potentially the variables)

### Steps To Reproduce

1. use latest graphiql 5 version
2. render component
3. write a query
4. click "Prettify Query" -> see error in console

### Environment

* GraphiQL Version: 5.2.0
* OS: ubuntu
* Browser: edge stable
* Bundler: vite
* `react` Version: 19

### Anything else?

_No response_