macOS: Skip tst_QGLThreads::renderInThread

It crashes in the render thread:

thread #7, name = 'SceneRenderingThread'
   frame #0: libsystem_kernel.dylib`__wait4_nocancel + 10
   frame #1: libsystem_c.dylib`system + 452
   frame #2: QtTest`stackTrace() + 325
   frame #3: QtTest`QTest::FatalSignalHandler::signal(int) + 207
   frame #4: libsystem_platform.dylib`_sigtramp + 26
   frame #5: libsystem_platform.dylib`_platform_bzero$VARIANT$Base + 23
   frame #6: GLRendererFloat`gldSetZero + 63
   frame #7: GLRendererFloat`gldClearDrawBuffer + 3792
   frame #8: GLRendererFloat`gldClearFramebufferData + 49
   frame #9: GLEngine`glClear_Exec + 541
   frame #10: tst_qglthreads`SceneRenderingThread::run() + 227

Task-number: QTBUG-68524
Change-Id: I6bc67cb342f77dc1a590a25af535f9bb7f0d325a
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

tests/auto/opengl/qglthreads/tst_qglthreads.cpp

@@ -355,6 +355,11 @@ void tst_QGLThreads::renderInThread()
     QFETCH(bool, resize);
     QFETCH(bool, update);
 
+#if defined(Q_OS_MACOS)
+    if (resize)
+        QSKIP("gldSetZero crashes in render thread, QTBUG-68524");
+#endif
+
     ThreadSafeGLWidget widget;
     widget.resize(200, 200);
     SceneRenderingThread thread(&widget);