tests: kernel: timer: timer_behavior: Reduce tick frequency(nrf54l09pdk)

 Test test_one_tick_timer_train was failing due not being able to
 execute enough 1 tick timeouts. Decrease system ticks frequency
 to make the test pass.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>