[Reg-5.15.2->6.3.0] Menu separators do not collapse after items moved with setMenuRole

When moving menu items with setMenuRole, menu separators collapse as expected in Qt 5.15.2 on macOS 11. In Qt 6.3.0, menu separators do not collapse.

This was observed when testing builds of OBS Studio with Qt 6.3.0. We believe that this behavior occurs after unfocusing and refocusing the Qt application window. See attached demo video.

I initially commented on QTBUG-40071 as that seemed to closely describe the behavior we're observing. After some further investigation, we think that this is due to one or both of the commits from QTBUG-88651 and QTBUG-94802, as when we apply both of those to Qt 5.15.2, the issue also appears.