tests: disable tests/lib/ringbuffer failing on qemu_arc_hs6x

Temporary disable tests/lib/ringbuffer failing tests on
qemu_arc_hs6x until we fix the rootcause so we can enable
qemu_arc_hs6x in upstream verification.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>