Gibibyte, not gigabyte

[alexispurslane]

Pointed out by @baskerville #28461.

[rust-highfive]

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[steveklabnik]

Thanks @ChristopherDumas ! Unfortunately, the reason that we moved that to an issue is that I closed #28441, until we figure out what we want to do. And if we do decide to resolve it, I would like @baskerville's original PR to get merged, since they had it first. Does that make sense?