rust: pin-init: replace clippy expect with allow

`clippy` has changed behavior in [1] (Rust 1.95) where it no longer
warns about the `let_and_return` lint when a comment is placed between
the let binding and the return expression. Nightly thus fails to build,
because the expectation is no longer fulfilled.

Thus replace the expectation with an `allow`.

[ The errors were:

      error: this lint expectation is unfulfilled
          --> rust/pin-init/src/lib.rs:1279:10
           |
      1279 | #[expect(clippy::let_and_return)]
           |          ^^^^^^^^^^^^^^^^^^^^^^
           |
           = note: `-D unfulfilled-lint-expectations` implied by `-D warnings`
           = help: to override `-D warnings` add `#[allow(unfulfilled_lint_expectations)]`

      error: this lint expectation is unfulfilled
          --> rust/pin-init/src/lib.rs:1295:10
           |
      1295 | #[expect(clippy::let_and_return)]
           |          ^^^^^^^^^^^^^^^^^^^^^^

    - Miguel ]

Link: rust-lang/rust-clippy#16461 [1]
Signed-off-by: Benno Lossin <lossin@kernel.org>
Cc: stable@vger.kernel.org # Needed in 6.18.y and later.
Link: https://patch.msgid.link/20260215132232.1549861-1-lossin@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: BennoLossin

rust/pin-init/src/lib.rs

@@ -1276,13 +1276,13 @@ pub const unsafe fn init_from_closure<T: ?Sized, E>(
 ///
 /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
 ///   pointer must result in a valid `U`.
-#[expect(clippy::let_and_return)]
 pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
     // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
     // requirements.
     let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
     // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
     // cycle when computing the type returned by this function)
+    #[allow(clippy::let_and_return)]
     res
 }
 
@@ -1292,13 +1292,13 @@ pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl Pin
 ///
 /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
 ///   pointer must result in a valid `U`.
-#[expect(clippy::let_and_return)]
 pub const unsafe fn cast_init<T, U, E>(init: impl Init<T, E>) -> impl Init<U, E> {
     // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
     // requirements.
     let res = unsafe { init_from_closure(|ptr: *mut U| init.__init(ptr.cast::<T>())) };
     // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
     // cycle when computing the type returned by this function)
+    #[allow(clippy::let_and_return)]
     res
 }