Rollup merge of #78788 - jhpratt:isize-impl-fix, r=m-ou-se
Rollup merge of #78788 - jhpratt:isize-impl-fix, r=m-ou-se

Correct unsigned equivalent of isize to be usize

See [#74913 (comment)](https://github.com/rust-lang/rust/issues/74913#issuecomment-722334456) for why this matters. Apparently it hasn't been used anywhere else, though CI will tell for sure.

aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust