Scroll wheel method deprecated in Pyside6? #146

When I try to use the scroll wheel in plotter I get the following error on stderr:

Traceback (most recent call last):
  File "/home/mgale/mambaforge/lib/python3.10/site-packages/openmc_plotter/plotgui.py", line 342, in wheelEvent
    if event.delta() and event.modifiers() == QtCore.Qt.ShiftModifier:
AttributeError: 'PySide6.QtGui.QWheelEvent' object has no attribute 'delta'

I'm assuming delta was deprecated at some point.

Versions of libraries:

• openmc-plotter==0.4.0
• PySide6==6.7.0
• PySide6_Addons==6.7.0
• PySide6_Essentials==6.7.0
• qtconsole==5.4.3

This is a small slice, I figured you didn't want my full pip freeze.