chore: add comment

Author: zhangzhonghe

packages/runtime-core/__tests__/hmr.spec.ts

@@ -538,6 +538,7 @@ describe('hot module replacement', () => {
     expect(serializeInner(root)).toBe('bar')
   })
 
+  // #6978
   test('rerender in change hoisted nodes', () => {
     const root = nodeOps.createElement('div')
     const appId = 'test-app-id'