fix build with rust 1.89

cf https://bugzilla.mozilla.org/show_bug.cgi?id=1982003

taken from:
https://github.com/openbsd/ports/commit/3ef8a2538893109bea8211ef13a870822264e096

--- third_party/rust/allocator-api2/src/stable/vec/mod.rs.orig	2025-08-13 22:43:24.000000000 +0200
+++ third_party/rust/allocator-api2/src/stable/vec/mod.rs	2025-09-01 08:52:19.103780000 +0200
@@ -51,6 +51,8 @@
 //!
 //! [`push`]: Vec::push
 
+#![warn(dangerous_implicit_autorefs)]
+
 #[cfg(not(no_global_oom_handling))]
 use core::cmp;
 use core::cmp::Ordering;