"panic! (the 'impossible' happened)" on 9.4 series

I'm getting `panic! (the 'impossible' happened)` on 9.4 series compilers when compiling `Cabal-syntax-3.14.0.0`. For example, [`stan` just failed](https://github.com/tomjaguarpaw/stan/actions/runs/11088132338/job/30807643954) on all of

- "9.4.1"
- "9.4.2"
- "9.4.4"
- "9.4.5"
- "9.4.6"

[EDIT: remove 9.4.7, because it actually works]

(`stan` doesn't support 9.4.3, and I haven't added 9.4.8 yet) and [`extensions` failed](https://github.com/kowainik/extensions/actions/runs/11085463260/job/30801906351) on 9.4.2.

9.4.8 seems to be fine (see https://github.com/kowainik/extensions/actions/runs/11085510928/job/30802009359).

Ultimately this is a GHC bug, but I'm reporting here for visibility.