test_MC16_FullG4MT_ttbar_MT.sh: Switch off diff-pool checks to previous nightlies
The order of events in the output file will vary from nightly to nightly. The order of events in the file can affect the root compression, so container sizes can fluctuate slightly. Therefore diff-pool can show a difference even if the contents of the containers for each event are the same.
NB This change is just to an ART script, so the CI output will be unaffected.