Updating diff_root_files.py to look for 'EventInfoAux.'

Hi guys,

Interestingly (to me) the xAOD::EventInfo information is stored as a CollectionTree attribute named xAOD::EventAuxInfo_v1_EventInfoAux. in upstream data formats but in AOD it's named EventInfoAux.. We simply check the latter if the former fails.

This fixes ATLASRECTS-5115.

Best, Serhan

cc : @mhodgkin @jchapman