[widgets][dataformateditor] Add parent to QMenu

Issue found when testing with PySide2.

From the documentation, QPushButton::setMenu
does not take ownership of the menu. With PySide2,
the menu is garbage collected but the actions
created from it are not completely destroyed as
it seems. Giving the menu a proper parent ensure
that its lifetime is correctly handled.
4 jobs for 248_fix_button_menu_lifetime in 10 minutes and 6 seconds (queued for 8 seconds)