Rollup merge of rust-lang#137764 - compiler-errors:always-applicable-negative-impl, r=lcnr

Ensure that negative auto impls are always applicable

r? lcnr (or reassign if you dont want to review)

rust-lang#68318 (comment)

Author: compiler-errors

core/src/convert/mod.rs

@@ -778,7 +778,6 @@ impl<T> From<T> for T {
 ///
 /// [#64715]: https://github.com/rust-lang/rust/issues/64715
 #[stable(feature = "convert_infallible", since = "1.34.0")]
-#[allow(unused_attributes)] // FIXME(#58633): do a principled fix instead.
 #[rustc_reservation_impl = "permitting this impl would forbid us from adding \
                             `impl<T> From<!> for T` later; see rust-lang/rust#64715 for details"]
 impl<T> From<!> for T {