gdi32/tests: Mark tests failing randomly on Windows as flaky.

dlls/gdi32/tests/driver.c

@@ -671,6 +671,7 @@ static void test_D3DKMTCheckOcclusion(void)
     ShowWindow(hwnd, SW_MINIMIZE);
     occlusion_desc.hWnd = hwnd;
     status = pD3DKMTCheckOcclusion(&occlusion_desc);
+    flaky
     ok(status == STATUS_SUCCESS, "Got unexpected return code %#lx.\n", status);
     ShowWindow(hwnd, SW_SHOWNORMAL);