Fix indent for convert_closure_to_fn

[A4-Tacks]

Example

fn foo() {
    {
        let closure = |$0| match () {
            () => {},
        };
        closure();
    }
}

Before this PR:

fn foo() {
    {
        fn closure() {
            match () {
                    () => {},
                }
        }
        closure();
    }
}

After this PR:

fn foo() {
    {
        fn closure() {
            match () {
                () => {},
            }
        }
        closure();
    }
}