QWidget::showMinimized only works once under Stage Manager

Steps to reproduce:

1. Make sure Stage Manager is turned on in System Settings
2. Build and run the attached minimum reproducible example app
3. Press Cmd + M to minimize the app into the Stage Manager side panel
4. Click on the minimized app to restore it
5. Press Cmd + M again. Nothing happens
6. Double click the title bar to maximize the window
7. Press Cmd + M again. The window is minimized

`showMinimized` seems to only work a single time after each window event.