QSortFilterProxyModel test: fix failing appearsAndSort

Testcase appearsAndSort failed when running the complete testcase but
not as single test. More irritating was the fact that the error was in
QAbstractItemModelTester::headerDataChanged() but the affected test did
not change any header nor does it use the blamed model...
The reason for this is, that QAbstractProxyModel emits a queued
headerDataChanged signal when the header item count changes and
therefore only evaluated when the event loop is run.
Fix it by calling processEvents() after the rowCount change in
filterColumns().
Amends 72e802f3b0

Pick-to: 6.6 6.5
Change-Id: I10cb5aa9c40a6925113cc9c23616774bf15784a4
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

tests/auto/corelib/itemmodels/qsortfilterproxymodel/tst_qsortfilterproxymodel.cpp

@@ -62,6 +62,7 @@ void tst_QSortFilterProxyModel::cleanup()
     m_proxy->sort(-1, Qt::AscendingOrder);
     m_model->clear();
     m_model->insertColumns(0, 1);
+    QCoreApplication::processEvents();  // cleanup possibly queued events
 }
 
 /*
@@ -1100,7 +1101,6 @@ void tst_QSortFilterProxyModel::filterColumns_data()
                              << "bravo"
                              << "lima")
                          << true;
-
     QTest::newRow("some") << "lie"
                           << (QStringList()
                               << "charlie"
@@ -1126,6 +1126,7 @@ void tst_QSortFilterProxyModel::filterColumns()
     // prepare model
     m_model->setColumnCount(initial.size());
     m_model->setRowCount(1);
+    QCoreApplication::processEvents();  // QAbstractProxyModel queues the headerDataChanged() signal
     QCOMPARE(m_model->columnCount(QModelIndex()), initial.size());
     QCOMPARE(m_model->rowCount(QModelIndex()), 1);
     // set data