Note: This information is meant for informational purposes only. You should always consult a qualified legal or accounting professional.
In most areas of the world, gift card sales are not considered "revenue" until they are redeemed (as opposed to when they are sold).
Shopify will take care of "holding" the money until the gift card is redeemed and also won't include them as sales in its reporting features until they are used.
That said, it's important to note that selling gift cards will generally not result in immediate cashflow (at least until the gift card is redeemed). Keep in mind, however, that selling gift cards early in the coronavirus crisis could help "stagger" cashflow to later, which could be important if the pandemic stretches more months.
We do have some tips on how to encourage users to redeem gift cards.