QTableView: fix moving rows by drag-n-drop

If we don't set dropEventMoved to true, then QAbstractItemView::startDrag
will delete the rows after the move (after QDrag::exec() returns).

Fixes: QTBUG-129128
Pick-to: 6.8.0
Change-Id: I85e7903a12b13c4b73e34fa1fcac56e50f421191
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit d2384783477e88190fb87287bb9af8ea9a46343e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/itemviews/qtableview.cpp

@@ -3165,8 +3165,10 @@ void QTableView::dropEvent(QDropEvent *event)
                     }
                     r = pIndex.row() + 1;   // Dropped items are inserted contiguously and in the right order.
                 }
-                if (dataMoved)
+                if (dataMoved) {
+                    d->dropEventMoved = true;
                     event->accept();
+                }
             }
         }
     }