[graphiql] Variables suggest doesn't seem to be working

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Current Behavior

I noticed that the variable suggest doesn't seem to work at all?
In the previous versions, the variable names would be auto -populated based on the variables of the query/mutation present in the selected tab.

This is not a show stopper but thought seems like one of those feature that can reduce some keystrokes.

### Expected Behavior

In the variables pane of the Grpahiql UI, the variables should be suggested depending on the variables defined for the query/mutation in the selected tab.

### Steps To Reproduce

1. Insert a graphql query which requires variables for one of its fields
2. Move to the variable pane below the query and provided values for the required variables.

### Environment

* GraphiQL Version: 5.2.0
* OS: MacOs 15.7.1
* Browser: Google Chrome 141.0.7390.123
* Bundler:
* `react` Version:
* `graphql` Version:

### Anything else?

_No response_