``#[rustfmt::skip]`` is ignored in struct impl.

Describe the bug

Using #[rustfmt::skip] to prevent damage to comments doesn’t work if the comment is
inside a struct impl.

To Reproduce

#[rustfmt::skip]
/** Comment.

    Rustfmt skips this as expected. */
fn main() {
    for _ in 1..Foo::getRandomNumber() {
        println!("Hello, world!");
    }
}

struct Foo;

impl Foo {
    #[rustfmt::skip]
    /** Comment.

        Rustfmt unindents this despite the ::skip above. */
    #[allow(non_snake_case)]
    pub fn getRandomNumber() -> i32 { 4 }
}

Expected behavior

The comment on getRandomNumber() should be left alone.

Meta

• rustfmt version: 1.4.20-stable
• From where did you install rustfmt?: from the Fedora 32 repos.
• How do you run rustfmt: doesn’t matter, both cargo fmt and rustfmt show the same defect.

No source files or tests are named. Start by running the provided reproducer with rustfmt and trace how #[rustfmt::skip] is handled on methods inside an impl. Done means the comment on getRandomNumber remains unchanged and a regression test covers the case.