Increase error ignore level when retrieving CutBookkeepers

Release notes

Quiet warnings when retrieving CutBookkeepers in TQxAODSkimmingAlgorithm

Details

There was already code temporarily changing gErrorIgnoreLevel to avoid a large number of warnings generated by TEvent in TQxAODSkimmingAlgorithm, but the warnings still appeared. I increased the value from kWarning to kError, so now they are actually suppressed. Matt, you wrote this in the first place (or at least touched it last), does this seem reasonable to you?