alloc: #[allow(instantly_dangling_pointer)] for a test about dangling pointers

Author: GrigorenkoPV

Diff for: library/alloc/tests/boxed.rs

@@ -4,6 +4,9 @@ use core::mem::MaybeUninit;
 use core::ptr::NonNull;
 
 #[test]
+// FIXME(GrigorenkoPV)
+#[allow(unknown_lints, reason="`instantly_dangling_pointer` does not exist at stage 0 yet")]
+#[allow(instantly_dangling_pointer)]
 fn uninitialized_zero_size_box() {
     assert_eq!(
         &*Box::<()>::new_uninit() as *const _,