Client: Update size hints on custom margins change

As size hints get sent in window content geometry,
they have to be updated once window content geometry changes

Pick-to: 6.7 6.5
Change-Id: I7c17770d29be8381b0c43ab724202219a9cf7a5f
Reviewed-by: David Edmundson <davidedmundson@kde.org>

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -889,6 +889,7 @@ QMargins QWaylandWindow::clientSideMargins() const
 void QWaylandWindow::setCustomMargins(const QMargins &margins) {
     const QMargins oldMargins = mCustomMargins;
     mCustomMargins = margins;
+    propagateSizeHints();
     setGeometry(geometry().marginsRemoved(oldMargins).marginsAdded(margins));
 }