TrigT1CTMonitoring: Fix retrieval of LVL1::NimCTP.
LVL1::NimCTP is now recorded as const. This caused retrieval here to fail, breaking q431. Change to retrieve it as const.
Note: this code had a pre-existing const_cast used to change the object in SG. This is not thread-safe. In practice, it's probably ok with the current configuration, but this should be rethought.