samples: timer_synchronization: exclude qemu_arc_hs5x

Exclude qemu_arc_hs5x from the test, seems to fail since f0daf904. Other
ARC platform works so let's exclude this one while the issue is
investigated.

Link: https://github.com/zephyrproject-rtos/zephyr/issues/62405


Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>