Update use of signals for QCheckBox

[magnesj]

NOTE! This is a fix for a new feature introduced in Qt 6.7

The following message is seen on Windows.

qt.core.qobject.connect: QObject::connect: Connecting from COMPAT signal (QCheckBox::stateChanged(int))

Related issue
https://forum.qt.io/topic/139073/no-matching-signal-and-no-matching-member-function-for-call-to-connect