Small suggestions to PySide6 tutorials

[imamedic]

• PySide6 Widgets
   QComboBox.NoInsert (or whatever policy) should likely be QComboBox.InsertPolicy.NoInsert
• super(MainWindow, self).__init__() could be super().__init__() throughout...as of Python3.0 super was changed to drop explicit naming of parent class source reference
• PySide6 Layouts  for n, color in enumerate(["red", "green", "blue", "yellow"]): could be for color in ["red", "green", "blue", "yellow"]
• in menus lesson label.setAlignment(Qt.AlignCenter) should likely be label.setAlignment(Qt.AlignmentFlag.AlignCenter)