Add typehint for DataModel in app.py

[klmcadams]

Add typehint for DataModel in app.py once ansys/pymechanical-stubs#93 is merged and a patch release of ansys-mechanical-stubs has been completed

Update this line to def DataModel(self) -> Ansys.Mechanical.DataModel.Interfaces.IDataModelObject (or DataModelObject since it points to IDataModelObject)

pymechanical/src/ansys/mechanical/core/embedding/app.py

Line 379 in 033053b

def DataModel(self):