non_snake_case lint does not fire on argument names in fn pointers

[theemathas]

I tried this code:

pub fn foo() {
    let _: fn(CamelCase: i32);
}

I expected rust to warn with the non_snake_case lint, due to the camel case argument. Instead, the code compiles without warnings.

See also #140088

Meta

Issue reproduces on the playground with version 1.88.0-nightly (2025-04-07 e643f59f6da3a84f43e7)