Notebook integration test broken "Opening a notebook should fire activeNotebook event changed only once"

```
  1) Notebook Editor
       Opening a notebook should fire activeNotebook event changed only once:
     AssertionError [ERR_ASSERTION] [ERR_ASSERTION]: undefined == true
      at Context.<anonymous> (extensions/vscode-api-tests/src/singlefolder-tests/notebook.editor.test.ts:84:10)
      at processTicksAndRejections (internal/process/task_queues.js:93:5)
```