[autotests] Fix testX11TimestampUpdate after latest change

We need to init the X11 standalone platform plugin now.

autotests/CMakeLists.txt

@@ -359,8 +359,10 @@ ecm_mark_as_test(testGestures)
 # Test X11 TimestampUpdate
 ########################################################
 add_executable(testX11TimestampUpdate test_x11_timestamp_update.cpp)
+target_compile_definitions(testX11TimestampUpdate PRIVATE KWINBACKENDPATH="${CMAKE_BINARY_DIR}/plugins/platforms/x11/standalone/KWinX11Platform.so")
 target_link_libraries(testX11TimestampUpdate
     Qt5::Test
+    KF5::CoreAddons
     kwin
 )
 add_test(kwin-testX11TimestampUpdate testX11TimestampUpdate)

autotests/test_x11_timestamp_update.cpp

@@ -21,6 +21,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QTest>
 #include <QX11Info>
 
+#include <KPluginMetaData>
+
 #include "main.h"
 #include "utils.h"
 
@@ -44,6 +46,7 @@ X11TestApplication::X11TestApplication(int &argc, char **argv)
 {
     setX11Connection(QX11Info::connection());
     setX11RootWindow(QX11Info::appRootWindow());
+    initPlatform(KPluginMetaData(QStringLiteral(KWINBACKENDPATH)));
 }
 
 X11TestApplication::~X11TestApplication()