When calling insertRows(), the model of the child items was not
correctly updated. insertRow() is behaving correctly.
Fixes: QTBUG-131372
Change-Id: I8b6aef7ab97887c6eb46eb21b992d76e4d59b3a0
Reviewed-by: David Faure <david.faure@kdab.com>
(cherry picked from commit 5bab8448feb2661f871e71d71a95afaffcb1656a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 3536eb32bf7e6b177fe600256dc9efd0ff653e36)