Fix issue with peeking at digitized detectors in RDO File Merging
Entries in the metadata dictionary are stored as strings, so should be evalulated before being used. This is already done for HITS File Peeking: https://gitlab.cern.ch/atlas/athena/-/blob/master/Simulation/SimuJobTransforms/python/HitsFilePeeker.py#L124
FYI @tadej