PySide6 DeprecationWarning of exec_

Hi,

exec_ function is deprecated in PySide6, so the common PyQt5/PySide2 code gets deprecated warning when QT_API=pyside6.

DeprecationWarning: 'exec_' will be removed in the future. Use 'exec' instead.
  sys.exit(app.exec_())

On the other hand, PyQt6 removes exec_ but QtPy provides exec_ for the compatibility. (#259) As a result, DeprecationWarning of exec_ occurs only when QT_API=pyside6. Which should this DeprecationWarning be addressed by QtPy or the user application? Note that print_ function of PySide6 may have the same problem.

[kumattau]

I sent PR: #287 to fix this issue.

[kumattau]

Note that print_ function of PySide6 may have the same problem.

I mistook about the print_ function of PySide6. Unlike exec_, PySide6/PySide2 does not have print function. They have print_ function only.

The summary is as follows.

Qt Bindings	PyQt5	PyQt6	PySide2	PySide6
exec_	v		v	deprecated
exec	v	v		v
print_	v		v	v
print	v	v

I think QtPy don’t have to do anything about print and print_ of PySide6 because print_ is available on PyQt5/PyQt6/PySide2/PySide6. (when QT_API=pyqt6, QtPy already has mapped print to print_)