fix feature gate and tracking issue

Author: RalfJung

library/core/src/mem/maybe_uninit.rs

@@ -405,7 +405,7 @@ impl<T> MaybeUninit<T> {
     /// (Notice that the rules around references to uninitialized data are not finalized yet, but
     /// until they are, it is advisable to avoid them.)
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
-    #[rustc_const_unstable(feature="maybe_uninit_as_ptr", issue = "none")]
+    #[rustc_const_unstable(feature = "const_maybe_uninit_as_ptr", issue = "75251")]
     #[inline(always)]
     pub const fn as_ptr(&self) -> *const T {
         // `MaybeUninit` and `ManuallyDrop` are both `repr(transparent)` so we can cast the pointer.
@@ -444,7 +444,7 @@ impl<T> MaybeUninit<T> {
     /// (Notice that the rules around references to uninitialized data are not finalized yet, but
     /// until they are, it is advisable to avoid them.)
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
-    #[rustc_const_unstable(feature="maybe_uninit_as_ptr", issue = "none")]
+    #[rustc_const_unstable(feature = "const_maybe_uninit_as_ptr", issue = "75251")]
     #[inline(always)]
     pub const fn as_mut_ptr(&mut self) -> *mut T {
         // `MaybeUninit` and `ManuallyDrop` are both `repr(transparent)` so we can cast the pointer.