tests: bsim: bap: fix race on ISO lost after audio received

[Copilot]

Late BT_ISO_FLAGS_LOST packets can arrive after the BAP Unicast Client sends a release but before the ASE state-change notification is received — the server has stopped streaming while the CIS is still active. Since valid_rx_cnt > 1U at end-of-test, this spuriously fails the RX callback in bap_stream_rx.c.

Change

• Guard the BT_ISO_FLAGS_LOST failure with !TEST_FLAG(flag_audio_received), mirroring the pre-existing pattern used one branch above for BT_ISO_FLAGS_ERROR. Once the minimum expected SDUs have been received, a late lost indication is expected and no longer fails the test.

if (info->flags & BT_ISO_FLAGS_LOST) {
    log_stream_err(test_stream, info, buf);

    if (test_stream->valid_rx_cnt > 1U &&
        !TEST_FLAG(test_stream->flag_audio_received)) {
        FAIL("ISO receive lost\n");
    }
}