Accept a QKeySequence.StandardKey and int where QKeySequence | str is currently accepted

[AWhetter]

Fixes #27

I've tested this by running mypy against the following code:

import sys
from PySide2 import QtCore, QtGui, QtWidgets

class Window(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self._label = QtWidgets.QLabel("Try Delete", self)
        self._shortcut = QtWidgets.QShortcut(QtGui.QKeySequence.StandardKey.Delete, self)
        self._shortcut.activated.connect(self.on_delete)

        self._layout = QtWidgets.QHBoxLayout()
        self._layout.addWidget(self._label)

        self.setLayout(self._layout)
        self.resize(150, 100)
        self.show()

    @QtCore.Slot()
    def on_delete(self):
        print("Deleting!")

app = QtWidgets.QApplication(sys.argv)
win = Window()
win.show()
sys.exit(app.exec_())

mypy fails without this change, and passes with the change.
I haven't tested every changed signature, but I've changed only those signatures that are similarly typed in PySide6.