I'm afraid I can't find any setting for it. And frankly, I don't really see much of a use case for such a setting. Generally a screenshot takes up between 100KB to 2,5MB, so you'd have to take at least ~ 400 screenshots just to get up to 1GB. Also deleting the screenshots would take like a minute, so it just seems like a nonissue.
What kind of scenario are you thinking of where this is probable?