ci: Switch back to default coreutils (uutils) after libffi-sys bump Now that Miri has updated to the latest `libffi-sys`, we should be able to remove the GNU coreutils workaround, and switch back to the default coreutils (uutils) in the runners using Ubuntu 25.10 images. If we encounter any other uutils compatibility problems in the future, they should hopefully be easier to trace back to specific changes. - https://github.com/rust-lang/rust/pull/147581 - https://github.com/rust-lang/miri/pull/4634 - https://github.com/rust-lang/rust/pull/147744 Closes rust-lang/rust#147556.