Ignore unreachable_pub false positives

[taiki-e]

https://github.com/rust-lang/futures-rs/runs/4783724442?check_suite_focus=true

error: unreachable `pub` item
   --> futures/src/lib.rs:180:29
    |
180 |     pub use crate::future::{FutureExt as _, TryFutureExt as _};
    |     ---                     ^^^^^^^^^^^^^^
    |     |
    |     help: consider restricting its visibility: `pub(crate)`
    |
    = note: `-D unreachable-pub` implied by `-D warnings`
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:180:45
    |
180 |     pub use crate::future::{FutureExt as _, TryFutureExt as _};
    |     ---                                     ^^^^^^^^^^^^^^^^^
    |     |
    |     help: consider restricting its visibility: `pub(crate)`
    |
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:184:29
    |
184 |     pub use crate::stream::{StreamExt as _, TryStreamExt as _};
    |     ---                     ^^^^^^^^^^^^^^
    |     |
    |     help: consider restricting its visibility: `pub(crate)`
    |
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:184:45
    |
184 |     pub use crate::stream::{StreamExt as _, TryStreamExt as _};
    |     ---                                     ^^^^^^^^^^^^^^^^^
    |     |
    |     help: consider restricting its visibility: `pub(crate)`
    |
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:192:9
    |
191 |     pub use crate::io::{
    |     --- help: consider restricting its visibility: `pub(crate)`
192 |         AsyncBufReadExt as _, AsyncReadExt as _, AsyncSeekExt as _, AsyncWriteExt as _,
    |         ^^^^^^^^^^^^^^^^^^^^
    |
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:192:31
    |
191 |     pub use crate::io::{
    |     --- help: consider restricting its visibility: `pub(crate)`
192 |         AsyncBufReadExt as _, AsyncReadExt as _, AsyncSeekExt as _, AsyncWriteExt as _,
    |                               ^^^^^^^^^^^^^^^^^
    |
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:192:50
    |
191 |     pub use crate::io::{
    |     --- help: consider restricting its visibility: `pub(crate)`
192 |         AsyncBufReadExt as _, AsyncReadExt as _, AsyncSeekExt as _, AsyncWriteExt as _,
    |                                                  ^^^^^^^^^^^^^^^^^
    |
    = help: or consider exporting it for use by other crates

error: unreachable `pub` item
   --> futures/src/lib.rs:192:69
    |
191 |     pub use crate::io::{
    |     --- help: consider restricting its visibility: `pub(crate)`
192 |         AsyncBufReadExt as _, AsyncReadExt as _, AsyncSeekExt as _, AsyncWriteExt as _,
    |                                                                     ^^^^^^^^^^^^^^^^^^
    |
    = help: or consider exporting it for use by other crates

[taiki-e]

It is interesting that only nested underscore imports are affected.