Fix mdfdump test

mdfdump.py was failing in the test because of the error

RunStampCheck       ERROR Database not up-to-date. No valid data for run 6718861 at 1970-01-01 00:00:00.0 UTC

and was printing twice the content of the same RawEvent.

The test was passing because, from the reference file, it was expecting the failure (it's not the first time I see this kind of issue).

I noticed the problem because with !3510 (merged) the RunStampCheck is implicitly disabled (it does not make sense in Run3), thus fixing the configuration error in mdfdump.py.