Qt 6.7 temp fix, change to Qt needed to fully fix

[mattkdab]

This change enables building with Qt 6.7, but assuming this Qt patch is approved, the following will no longer be needed:

+ #if QT_VERSION < QT_VERSION_CHECK(6, 7, 0)
    MO_ADD_METAOBJECT1(QDeferredDeleteEvent, QEvent);
    MO_ADD_PROPERTY_RO(QDeferredDeleteEvent, loopLevel);
+ #endif

So while this works for now, it should not be the real final solution.

Eventually fixes #918

[CLAassistant]

All committers have signed the CLA.

[winterz]

this is hard to verify until we add qt 6.7 to the CI matrix

@dantti

[dantti]

With the current 6.7 beta that Qt company released it still fails:
https://github.com/KDAB/GammaRay/actions/runs/7550206827/job/20555459025

[mattkdab]

If the patch at https://codereview.qt-project.org/c/qt/qtbase/+/531661 is merged, it should enable the reversion of this part of the change:

+ #if QT_VERSION < QT_VERSION_CHECK(6, 7, 0)
    MO_ADD_METAOBJECT1(QDeferredDeleteEvent, QEvent);
    MO_ADD_PROPERTY_RO(QDeferredDeleteEvent, loopLevel);
+ #endif

@redstrate has already tested this

[mattkdab]

With the current 6.7 beta that Qt company released it still fails: https://github.com/KDAB/GammaRay/actions/runs/7550206827/job/20555459025

It should pass for this PR only at this point