Fix windows custom margins key mistake

Sine Striker

2023-12-09 7aabc22e0b6841a46eb449398e4e8910352008cc

 examples/mainwindow/mainwindow.cpp

@@ -99,5 +99,6 @@
    setMenuWidget(windowBar);
    setCentralWidget(clockWidget);
    setWindowTitle("Example MainWindow");
    // setContentsMargins({0, 1, 0, 0});
    resize(640, 480);
}