unused variable linter sometimes warns on _, even though _x suppresses the linter

[kim-em]

Steps to Reproduce

open List

example [Inhabited α] : ∀ {l : List α}, head? l = some a → head! l = a
  | _ :: _, rfl => rfl
--  ^--- unused variable `a`

The linter does not complain on

open List

example [Inhabited α] : ∀ {l : List α}, head? l = some a → head! l = a
  | _a :: _, rfl => rfl

Versions

nightly-2024-09-04

[Kha]

Looks like a duplicate of #2830