Building against fmt v11 does not work

This is not extremely critical I think. However, since I just stumbled over it and couldn't come up with a < 30 min fix for it, I figured I at least write it down somewhere. Gaudi doesn't currently build against fmt v11, because the detail::error_handler has been removed in this commit

The only use I could find is in https://gitlab.cern.ch/gaudi/Gaudi/-/blob/master/GaudiKernel/include/Gaudi/PropertyFmt.h