`unused_variables` lint fires for E0005 error

[ehuss]

E0005 has started issuing warnings for unused variables. It seems to just add noise, since the code is incorrect, the warning is a little misguided.

fn main() {
    let x = Some(1);
    let Some(y) = x; //~ ERROR E0005
}

displays:

error[E0005]: refutable pattern in local binding: `None` not covered
  --> E0005.rs:3:9
   |
LL |     let Some(y) = x; //~ ERROR E0005
   |         ^^^^^^^ pattern `None` not covered

warning: unused variable: `y`
  --> E0005.rs:3:14
   |
LL |     let Some(y) = x; //~ ERROR E0005
   |              ^ help: consider prefixing with an underscore: `_y`
   |
   = note: #[warn(unused_variables)] on by default

This started in #59050. I can't really tell which PR in that rollup is responsible.

This is a pretty minor issue, and perhaps issuing warnings makes more sense in other cases. Feel free to close this if it doesn't seem like an issue.