test(swingset): use xs-worker to avoid gc flake (#10085)

closes: #10071

## Description

I believe #8695 introduced a dependency of the boostrap vat of this test on the gc behavior of the engine, which makes it flaky. Applies the common fix to use an xs-worker instead.

### Security Considerations
None

### Scaling Considerations
None

### Documentation Considerations
None

### Testing Considerations
Hopefully the flake is gone

### Upgrade Considerations
None

packages/SwingSet/test/gc-kernel.test.js

@@ -1031,7 +1031,7 @@ test('terminated vat', async t => {
       bootstrap: {
         sourceSpec: new URL('gc-dead-vat/bootstrap.js', import.meta.url)
           .pathname,
-        creationOptions: { managerType: 'local' },
+        creationOptions: { managerType: 'xs-worker' },
       },
     },
     bootstrap: 'bootstrap',