In this unofficial tweet, Jeremy Crawford states that the prerequisite ability scores for multiclassing are intended to be met by your base score and not a temporary score. As such, we can infer that magic items that don't permanently increase your ability scores wouldn't work.
Keith
@mikemearls @JeremyECrawford would a temporary stat bump fulfill a multi-class pre-req or does the base score have to meet the #
Jeremy
The intent is that your base score, not a temporary score, has to meet a multiclassing prerequisite.
This has also been reiterated in the official sage advice compendium:
Would a temporary stat bump fulfill a multiclass prerequisite, or does the base score have to meet the requirement? Your base score, not a temporary score, has to meet a multiclassing prerequisite.