"cargo miri test" now supports workspace

`cargo miri test` recently was made much more compatible with `cargo test`, and now supports workspaces in the same way. While checking GitHub for projects that need adjustment to the new way of passing flags to Miri, I stumbled upon this one which does not need updating but has a comment saying "cargo-miri does not support workspaces yet", so I figured I'd leave a note. :)

Search the repository for the comment stating that cargo-miri does not support workspaces. Read the surrounding usage or testing documentation, then update the outdated statement so it reflects current workspace support; done means no misleading claim remains.

Written by the indexing model from the issue text.