Detached QDockWidget with disabled DockWidgetClosable feature creates a window with _NET_WM_ACTION_CLOSE

When running the attached program with the GNOME window manager a detached dock widget is still closeable by the user despite disabled DockWidgetClosable feature.

Steps to reproduce:

• run main.cpp with GNOME window manager
• detach the dock widget
• click the X close button on the detached title bar
• try to reopen the dock using the menubar action

Actual result:

• the dock closes, and cannot reopened because the menubar action is disabled

Expected result:

• the dock refuses to close
• or: the menubar action is enabled and works