[graphiql] variables and headers do not load on first default tab

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

If you define `defaultTabs` with `variables` and/or `headers` set on the first tab it still won't get rendered (at least not on first load).

### Expected Behavior

Variables and headers render on initial page load like normal.

### Steps To Reproduce

demo.html

Based on [graphiql/examples/graphiql-cdn/index.html at main · graphql/graphiql](https://github.com/graphql/graphiql/blob/85edb9e0505db8ff963c9ad4674bc8fa2e02a35a/examples/graphiql-cdn/index.html):

```html

GraphiQL

body {
height: 100%;
margin: 0;
width: 100%;
overflow: hidden;
}

#graphiql {
height: 100vh;
}

const root = ReactDOM.createRoot(document.getElementById("graphiql"));
const fetcher = GraphiQL.createFetcher({
url: "https://swapi-graphql.netlify.app/.netlify/functions/index",
headers: { "X-Example-Header": "foo" },
});
const explorerPlugin = GraphiQLPluginExplorer.explorerPlugin();
root.render(
React.createElement(GraphiQL, {
fetcher,
defaultEditorToolsVisibility: true,
plugins: [explorerPlugin],
defaultTabs: [
{
query: `\
query FirstStarships($first: Int) {
allStarships(first: $first) {
starships {
name
model
}
}
}`,
variables: JSON.stringify(
{
first: 10,
},
null,
" "
),
headers: JSON.stringify(
{
"X-Special": "42",
},
null,
" "
),
},
{
query: `\
query FirstStarships2($first: Int) {
allStarships(first: $first) {
starships {
name
model
}
}
}`,
variables: JSON.stringify(
{
first: 10,
},
null,
" "
),
headers: JSON.stringify(
{
"X-Special": "42",
},
null,
" "
),
}
],
})
);

```

Initial load
After moving to second tab
After returning to first tab




### Environment

* GraphiQL Version: latest
* OS: macOS 13.5
* Browser: Microsoft Edge Version 115.0.1901.188 (Official build) (arm64)
* Bundler: unpkg.com
* `react` Version: 18
* `graphql` Version: transitive

### Anything else?

I first noticed this when loading multiple default tabs but the scenario is worse with a single default tab: the variables and headers don't display and there's no tab to move to and then return from to get the variables and headers to display