macOS: Enter in combo-box pop-up closes the whole dialog

Seen on macOS, but not reproduced on Windows.

When a combo-box pop-up is shown in a modal dialog and I hit the Enter key, just the pop-up closed in Qt 5.14 and older. Whereas in 6.3.1 and 6.6.1, the whole dialog closes, because the Enter also "hits" the default button. Thus it got broken somewhere between 5.14 and 6.3.1.