tests: bsim: cap_broadcast_reception: Workaround time dependent issue

This test is overly sensitive to the relative timing of the devices
and/or their random number generation.
Due to this the test failed with its current setup when chanding the
random generation for the nrf54.
Let's work around it by offsetting a bit one of the devices.
This is a provisional workaround until the underlying issue is
addressed.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>