Add another warning from ThorBPVLTIME to the exclusion list

Add the 'negative variance' warning from ThorBPVLTIME (which seems to happen on x86_64_v2, but not, or at least less on x86_64_v3) following Rec!2668 (merged) to the exclusion list. Improvements aimed at fixed both warnings now on the expulsion list are tracked by issue Rec#265.