mut in slice pattern: `[_, mut @ ..] = &[...]` is not needed?

Might be related to https://github.com/rust-lang/rust/issues/123076

Code

fn foo(s: &[usize]) {
    let [a, b @ ..] = s else {panic!()};
    let [a, mut b @ ..] = s else {panic!()};
}

Current output

error[E0277]: the size for values of type `[usize]` cannot be known at compilation time
 --> src/lib.rs:3:13
  |
3 |     let [a, mut b @ ..] = s else {panic!()};
  |             ^^^^^^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `Sized` is not implemented for `[usize]`
  = note: all local variables must have a statically known size
  = help: unsized locals are gated as an unstable feature

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` (lib) due to 1 previous error

Desired output

3 |     let [a, mut b @ ..] = s else {panic!()};
  |             ^^^^^^^^^^ doesn't have a size known at compile-time
                ^^^ help: remove this `mut` because ...

Rationale and extra context

I use mut b @ .. because I would like to change b later.
But removing mut makes it compile. So my thoughts are misleading.

Other cases

No response

Rust Version

Nightly version: 1.81.0-nightly

(2024-06-18 8fcd4dd08e2ba3e922d9)

Anything else?

No response

Start by reproducing the provided slice-pattern snippet on the stated nightly compiler and compare the diagnostics for [_, b @ ..] and [_, mut b @ ..]. Trace the compiler diagnostic path for E0277 and determine where the requested help suggestion would be tested. Done means the invalid mut case reports a targeted suggestion while the valid case continues to compile.