Fix nyc compile error (microsoft#14402)

Author: joyceerhl

src/test/datascience/notebook/helpers.unit.test.ts

@@ -31,7 +31,7 @@ suite('DataScience - NativeNotebook helpers', () => {
  ];
 
  // tslint:disable-next-line: no-any
- const notebook = notebookModelToVSCNotebookData(true, {}, Uri.file(''), cells, PYTHON_LANGUAGE);
+ const notebook = notebookModelToVSCNotebookData(true, {}, Uri.file(''), cells as any, PYTHON_LANGUAGE);
 
  assert.isOk(notebook);
  assert.deepEqual(notebook.languages, ['*']);