Bump rustc to remove ShallowInitBox

[N1ark]

Continuation of #1030
Fixes #973
Related to rust-lang/rust#148190

This is missing a transformation pass to make vec! safe. For the following original MIR:

((((*_4)).1).0).0 = [move _5]
storage_dead(_5)
_3 = move _4
conditional_drop[{impl Destruct for alloc::boxed::Box<T>[@TraitClause0, @TraitClause1]}<MaybeUninit<[u8; 1 : usize]>[{built_in impl Sized for [u8; 1 : usize]}], Global>[{built_in impl MetaSized for MaybeUninit<[u8; 1 : usize]>[{built_in impl Sized for [u8; 1 : usize]}]}, {built_in impl Sized for Global}]] _4
storage_dead(_4)
vec_2 = box_assume_init_into_vec_unsafe<u8, 1 : usize>[{built_in impl Sized for u8}](move _3)

we want something akin to

_T = [move _5]
_3 = Box::write(move _4, move _T)
_B = unsize<Box<[T; N]>, Box<[T]>>(move _3)
vec_2 = std::slice::{impl}::into_vec(move _B)