`PhantomPinned` warns that field is never read, but `PhantomData` does not

I tried this code:

```rust
use core::marker::{PhantomData, PhantomPinned};

struct Test {
    pin: PhantomPinned,
    data: PhantomData<()>,
}

fn main() {
    let _ = Test { pin: PhantomPinned, data: PhantomData };
}
```

This should not show any errors indicating that `pin` was not read, since its purpose is merely to avoid an `Unpin` impl. Instead, I get this output:

```
warning: field `pin` is never read
 --> src/main.rs:4:5
  |
3 | struct Test {
  |        ---- field in this struct
4 |     pin: PhantomPinned,
  |     ^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default
```

Note that `PhantomData` is specially handled to not do this, and I would expect `PhantomPinned` to act the same.

### Meta


`rustc --version --verbose`:
```
rustc 1.96.0-nightly (55e86c996 2026-04-02)
binary: rustc
commit-hash: 55e86c996809902e8bbad512cfb4d2c18be446d9
commit-date: 2026-04-02
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.2
```

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`PhantomPinned` warns that field is never read, but `PhantomData` does not #154888

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`PhantomPinned` warns that field is never read, but `PhantomData` does not #154888