ices/66906.rs: fixed with no errors

=== stdout ===
=== stderr ===
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> /home/runner/work/glacier/glacier/ices/66906.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default

warning: method is never used: `const_index`
  --> /home/runner/work/glacier/glacier/ices/66906.rs:10:5
   |
10 | /     fn const_index<const I: usize>(_: <Self as ConstInput<I>>::Input)
11 | |     where
12 | |         Self: ConstInput<I>
13 | |     {}
   | |______^
   |
   = note: `#[warn(dead_code)]` on by default

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