Auto merge of #120092 - zetanumbers:pin_in_static_allocator, r=Amanieu

Add `A: 'static` bound for `Arc/Rc::pin_in`

Analogous to rust-lang/rust#79327
Needed to preserve pin's [drop guarantee](https://doc.rust-lang.org/std/pin/index.html#drop-guarantee)

Author: bors