fix #[cfg(test)] warnings

src/liballoc/heap.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(not(test))]
 use core::ptr::PtrExt;
 
 // FIXME: #13996: mark the `allocate` and `reallocate` return value as `noalias`