Unable to set "delay" on UITester

We are seeing the following exception when we try to set `UITester(registries=..., delay=1000)`

```
...
File "C:\Users\rporuri\.edm\envs\...\lib\site-packages\traitsui\testing\tester\ui_wrapper.py", line 247, in perform
self._perform_or_inspect(interaction)
File "C:\Users\rporuri\.edm\envs\...\lib\site-packages\traitsui\testing\tester\ui_wrapper.py", line 313, in _perform_or_inspect
return handler(self, interaction)
File "C:\Users\rporuri\.edm\envs\...\lib\site-packages\traitsui\testing\tester\_ui_tester_registry\qt4\_traitsui\ui_base.py", line 33, in
lambda wrapper, _: _interaction_helpers.mouse_click_qwidget(
File "C:\Users\rporuri\.edm\envs\...\lib\site-packages\traitsui\testing\tester\_ui_tester_registry\qt4\_interaction_helpers.py", line 119, in mouse_click_qwidget
QTest.qSleep(delay)
AttributeError: type object 'PySide6.QtTest.QTest' has no attribute 'qSleep'
```