[layouts] Refresh layout automatically on page size/orientation change

Fixes #21624

Author: nyalldawson

src/app/layout/qgslayoutpagepropertieswidget.cpp

@@ -167,6 +167,7 @@ void QgsLayoutPagePropertiesWidget::updatePageSize()
   mPage->layout()->pageCollection()->endPageSizeChange();
   mPage->layout()->undoStack()->endMacro();
 
+  refreshLayout();
   emit pageOrientationChanged();
 }