Rollup merge of #120101 - mj10021:issue-120090-fix, r=WaffleLapkin

change `.unwrap()` to `?` on write where `fmt::Result` is returned

Fixes #120090 which points out that some of the `.unwrap()`s in `rustc_middle/src/mir/pretty.rs` are likely meant to be `?`s

Author: matthiaskrgr