TypeError: unsupported operand type(s) for &: 'int' and 'KeyboardModifier' for PySide6

We are using `enable` together with `chaco` and `traits` in `PySide6` application with Python 3.10. On both macOS and Windows, stderr gets flooded with `TypeError` from `BaseWindow._create_mouse_event()`:

```
Traceback (most recent call last):
File "enable\qt4\base_window.py", line 270, in leaveEvent
File "enable\qt4\base_window.py", line 148, in leaveEvent
File "enable\abstract_window.py", line 349, in _handle_mouse_event
File "enable\qt4\base_window.py", line 515, in _create_mouse_event
TypeError: unsupported operand type(s) for &: 'int' and 'KeyboardModifier'
```

The respective code reads `alt_down=bool(modifiers & QtCore.Qt.AltModifier),` and it seems that the problem is that many enums from the current `PySide6` implementation do not automatically convert to `int`.

It could be sufficient to use `.value()` to get the `int` value just like this:

```
alt_down=bool(modifiers & QtCore.Qt.AltModifier.value),
```

These are the versions we use:
- PySide6==6.4.0
- enable==5.3.1
- Python 3.10.8