ices/58987-4.rs: fixed with errors

[github-actions]

Issue: rust-lang/rust#58987

pub struct Matrix<T, const R: usize, const C: usize> {
    inner: [T; R * C]
}

fn main() {}

=== stdout ===
=== stderr ===
error: generic parameters may not be used in const operations
 --> /home/runner/work/glacier/glacier/ices/58987-4.rs:2:16
  |
2 |     inner: [T; R * C]
  |                ^ cannot perform const operation using `R`
  |
  = help: const parameters may only be used as standalone arguments, i.e. `R`
  = help: use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` to allow generic const expressions

error: generic parameters may not be used in const operations
 --> /home/runner/work/glacier/glacier/ices/58987-4.rs:2:20
  |
2 |     inner: [T; R * C]
  |                    ^ cannot perform const operation using `C`
  |
  = help: const parameters may only be used as standalone arguments, i.e. `C`
  = help: use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` to allow generic const expressions

error: aborting due to 2 previous errors

==============

[JohnTitor]

This one seems to be uncovered but some issues should cover, I presume.