gh-88496: IDLE - fix another test on macOS (#104075)

Needed for Catalina: test_sidebar add 'idletasks' and skip assert.

Author: terryjreedy

Lib/idlelib/idle_test/test_sidebar.py

@@ -57,7 +57,7 @@ def setUpClass(cls):
  @classmethod
  def tearDownClass(cls):
  cls.editwin.per.close()
- cls.root.update()
+ cls.root.update_idletasks()
  cls.root.destroy()
  del cls.text, cls.text_frame, cls.editwin, cls.root
 
@@ -695,7 +695,8 @@ def test_mousewheel(self):
  delta = -1 if sys.platform == 'darwin' else 120
  sidebar.canvas.event_generate('<MouseWheel>', x=0, y=0, delta=delta)
  yield
- self.assertIsNone(text.dlineinfo(text.index(f'{last_lineno}.0')))
+ if sys.platform != 'darwin': # .update_idletasks() does not work.
+ self.assertIsNone(text.dlineinfo(text.index(f'{last_lineno}.0')))
 
  # Scroll back down using the <Button-5> event.
  sidebar.canvas.event_generate('<Button-5>', x=0, y=0)