Stabilize const-weak-new

Bump its stabilization version several times along
the way to accommodate changes in release processes.

Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Co-authored-by: Trevor Gross <t.gross35@gmail.com>

Author: 3 people

library/alloc/src/rc.rs

@@ -2112,7 +2112,7 @@ impl<T> Weak<T> {
     /// assert!(empty.upgrade().is_none());
     /// ```
     #[stable(feature = "downgraded_weak", since = "1.10.0")]
-    #[rustc_const_unstable(feature = "const_weak_new", issue = "95091", reason = "recently added")]
+    #[rustc_const_stable(feature = "const_weak_new", since = "CURRENT_RUSTC_VERSION")]
     #[must_use]
     pub const fn new() -> Weak<T> {
         Weak { ptr: unsafe { NonNull::new_unchecked(ptr::invalid_mut::<RcBox<T>>(usize::MAX)) } }

library/alloc/src/sync.rs

@@ -1743,7 +1743,7 @@ impl<T> Weak<T> {
     /// assert!(empty.upgrade().is_none());
     /// ```
     #[stable(feature = "downgraded_weak", since = "1.10.0")]
-    #[rustc_const_unstable(feature = "const_weak_new", issue = "95091", reason = "recently added")]
+    #[rustc_const_stable(feature = "const_weak_new", since = "CURRENT_RUSTC_VERSION")]
     #[must_use]
     pub const fn new() -> Weak<T> {
         Weak { ptr: unsafe { NonNull::new_unchecked(ptr::invalid_mut::<ArcInner<T>>(usize::MAX)) } }