Hmm, doesn't transmute work on const generic arrays?

Trying:

```rust
            #[cfg(loom)]
            let mut result_cells: [Cell<T>; N] = {
                let cells: [MaybeUninit<Cell<T>>; N] = [const { MaybeUninit::uninit() }; N];
                for cell in cells.iter_mut() {
                    cell.write(Cell::new(0));
                }
                unsafe { core::mem::transmute(cells) }
            };
```

and getting:

```
error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
   --> src/mpmc.rs:172:26
    |
172 |                 unsafe { core::mem::transmute(cells) }
    |                          ^^^^^^^^^^^^^^^^^^^^
    |
    = note: source type: `[MaybeUninit<mpmc::Cell<T>>; N]` (this type does not have a fixed size)
    = note: target type: `[mpmc::Cell<T>; N]` (this type does not have a fixed size)

```