2D: Add QT_NAMESPACE to pierenderer.cpp

PieRenderer didn't have QT_BEGIN_NAMESPACE and QT_END_NAMESPACE.

Pick-to: 6.8
Change-Id: I70514460f89cb189a7a5cc75839d4e3098afa612
Reviewed-by: Sami Varanka <sami.varanka@qt.io>
(cherry picked from commit 43c7180d21)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit a3d9820da0)

src/graphs2d/qsgrenderer/pierenderer.cpp

@@ -13,6 +13,8 @@
 #include <private/qquickshape_p.h>
 #include <private/qquicksvgparser_p.h>
 
+QT_BEGIN_NAMESPACE
+
 PieRenderer::PieRenderer(QGraphsView *graph)
     : QQuickItem(graph)
     , m_graph(graph)
@@ -401,3 +403,5 @@ void PieRenderer::onPressedChanged()
         }
     }
 }
+
+QT_END_NAMESPACE