Give defaults to the built-in default query test a 20s timeout (#4268)

## Summary

Times out at the default 9s on every CI run since Vitest 4 landed
(#4260). It's the only test in `GraphiQL.spec.tsx` that boots Monaco's
`editorWorkerService` from a cold start; the rest get a warm worker.
Vitest 4's pool switch from `threads` to `forks` pushed cold-boot just
past 9s.

Bumped to 20s on this one test, with an inline comment explaining why
for the next person.

Failed on two back-to-back runs of an unrelated PR:
-
https://github.com/graphql/graphiql/actions/runs/25878177678/job/76051305013
-
https://github.com/graphql/graphiql/actions/runs/25878177678/job/76052552437

Author: trevor-scheer

packages/graphiql/src/GraphiQL.spec.tsx

@@ -167,6 +167,7 @@ describe('GraphiQL', () => {
   }); // schema
 
   describe('default query', () => {
+    // First test to boot Monaco's editor worker; cold start needs extra time under Vitest 4's forks pool.
     it('defaults to the built-in default query', async () => {
       const { container } = render(<GraphiQL fetcher={noOpFetcher} />);
 
@@ -177,7 +178,7 @@ describe('GraphiQL', () => {
         expect(queryEditor).toBeVisible();
         expect(queryEditor!.textContent).toBe('# Welcome to GraphiQL');
       });
-    });
+    }, 20000);
 
     it('accepts a custom default query', async () => {
       const { container } = render(