fix build of qmldesigner coretests against namespaced qt

Change-Id: I6fcd87a4f1a3e59994ca13d559a215b789f02e96
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@theqtcompany.com>

tests/auto/qml/qmldesigner/coretests/tst_testcore.cpp

@@ -86,6 +86,8 @@ using namespace QmlDesigner;
 #  define SHARE_PATH "/share/qtcreator"
 #endif
 
+QT_BEGIN_NAMESPACE
+
 //Allow comparison of QByteArray and QString. We always assume utf8 as the encoding.
 namespace QTest {
  bool qCompare(const QString &string, const QByteArray &array, const char *actual,
@@ -103,6 +105,8 @@ namespace QTest {
 
 }
 
+QT_END_NAMESPACE
+
 QString resourcePath()
 {
     return QDir::cleanPath(QTCREATORDIR + QLatin1String(SHARE_PATH));