[skip modfiles] Update BlackList_caches.txt
temporary remove blacklisting MG in 21.6.40 (needed to run https://prodtask-dev.cern.ch/prodtask/inputlist_with_request/47317/)
temporary remove blacklisting MG in 21.6.40 (needed to run https://prodtask-dev.cern.ch/prodtask/inputlist_with_request/47317/)