PyJobTransforms: Validating ROOT file require presence of event data
Tools/PyJobTransforms/python/trfValidateRootFile.py: In checkFile function, exit with error if file does not contain TTree or RNTuple with event data Tools/PyJobTransforms/python/trfArgClasses.py: Make metadataKeys mutable in case of str
Related to ATEAM-995
cc: tovsiann