Reborrow mut slice instead of converting it with as_ref

Co-authored-by: Noah Lev <camelidcamel@gmail.com>

library/core/src/array/mod.rs

@@ -184,7 +184,7 @@ fn borrow_mut(&mut self) -> &mut [T] {
     type Error = TryFromSliceError;
 
     fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
-        <Self>::try_from(slice.as_ref())
+        <Self>::try_from(&*slice)
     }
 }