test(editor): reduce flaky in turbo renderer test (#11973)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **Tests**
  - Improved test resource cleanup for the viewport turbo renderer, ensuring proper teardown after each test for more reliable and isolated test execution.
  - Enhanced stability by preventing errors during cleanup when certain elements or editors are absent.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/integration-test/src/__tests__/edgeless/turbo-renderer.spec.ts

@@ -8,7 +8,7 @@ import {
   ViewportTurboRendererExtension,
 } from '@blocksuite/affine-gfx-turbo-renderer';
 import { firstValueFrom } from 'rxjs';
-import { beforeEach, describe, expect, test } from 'vitest';
+import { afterEach, beforeEach, describe, expect, test } from 'vitest';
 
 import { wait } from '../utils/common.js';
 import { addSampleNotes } from '../utils/doc-generator.js';
@@ -19,8 +19,10 @@ import {
 } from '../utils/setup.js';
 
 describe('viewport turbo renderer', () => {
+  let cleanup: () => void;
+
   beforeEach(async () => {
-    const cleanup = await setupEditor('edgeless', [
+    cleanup = await setupEditor('edgeless', [
       ParagraphLayoutHandlerExtension,
       TurboRendererConfigFactory({
         painterWorkerEntry: createPainterWorker,
@@ -30,6 +32,8 @@ describe('viewport turbo renderer', () => {
     return cleanup;
   });
 
+  afterEach(() => cleanup?.());
+
   test('should render 6 notes in viewport', async () => {
     addSampleNotes(doc, 6);
     await wait();

blocksuite/integration-test/src/__tests__/utils/setup.ts

@@ -129,13 +129,13 @@ export async function setupEditor(
   const appElement = await createEditor(collection, mode, extensions);
 
   return () => {
-    appElement.remove();
+    appElement?.remove();
     cleanup();
   };
 }
 
 export function cleanup() {
-  window.editor.remove();
+  window.editor?.remove();
 
   delete (window as any).collection;