`&pin!()` stopped being deref-coerced in rust 1.88

I expected the following code to compile, since Pin implements Deref, so it should be possible to do a deref coercion from the type &Pin<i32> to the type &i32.

fn main() {
    let _x: &i32 = &std::pin::pin!(1i32);
}

The above code compiles without errors in rust 1.87.0. However, it produces the following compile error in rust 1.88.0

error[E0308]: mismatched types
 --> <source>:2:21
  |
2 |     let _x: &i32 = &std::pin::pin!(1i32);
  |                     ^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `Pin<&mut i32>`
  |
  = note: expected type `i32`
           found struct `Pin<&mut i32>`
  = note: this error originates in the macro `std::pin::pin` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.

This presumably regressed in #139114, which changed pin!() to use super let. This uses a block expression in the syntax, which then presumably runs into the bug in #23014.

I don't know if there are any realistic use cases which run into this problem. (Hopefully not.)

cc @dianne @m-ou-se (who worked on super let).

cc @jackh726 (who seemed to have recently been working on coercions).

Meta

Tested on Godbolt with rustc versions 1.87.0 and 1.88.0.

Reproduce the snippet with rustc 1.87.0 and 1.88.0, then inspect the pin!() change in #139114 and the block-expression coercion issue in #23014. Done means the reported reference coercion works again without regressing the super let behavior.