`clippy::uninlined-format-args` is quite complainy

Our Rust-Latest CI is now failing with warnings like this:

error: variables can be used directly in the `format!` string
   --> crates/fs-mistrust/src/walk.rs:189:21
    |
189 |                     format!("Current directory {:?} was not absolute.", cwd),
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args

I'm not enthused about this warning: I suggest that we disable it.

(One mystery to me is why we didn't spot this in rust-nightly)