tests: Bluetooth: CAP: Add bcast reception with multiple acceptors

Expand the CAP broadcast reception test to also run with
multiple acceptors to better verify correctness in the
procedures.

For this to run more stable, the maximum number of streams
has been reduce to 2, rather than
CONFIG_BT_BAP_BROADCAST_SRC_STREAM_COUNT.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>