Panic ltPSize
## Summary
Write a brief description of the issue.
## Steps to reproduce
- Compile GHC at https://gitlab.haskell.org/chrismwendt/ghc/-/tree/994062840b5c77c76dfed0644ac4059d7e2de136. That commit is only one tiny commit ahead of this commit on upstream's master: https://gitlab.haskell.org/ghc/ghc/-/tree/ee17001e54c3c6adccc5e3b67b629655c14da43a.
- Clone and checkout https://github.com/chrismwendt/ghci-reload-error-monadic-bang/tree/dd610a35522ffc265bf72c58cc3717d4a1fb4101
Run a `stack build` with that GHC version on the path:
```
$ ls -lh bin
total 0
lrwxr-xr-x 1 chrismwendt staff 67B Mar 16 02:25 ghc-9.4.4@ -> /Users/chrismwendt/gitlab.haskell.org/ghc/ghc/_build/stage1/bin/ghc
$ env PATH="$PWD/bin:$PATH" stack build
Warning: Stack has not been tested with GHC versions above 9.4, and using 9.7.20230316, this may fail.
Warning: Stack has not been tested with Cabal versions above 3.8, but version 3.9.0.0 was found, this may fail.
Warning: WARNING: Ignoring monadic-bang's bounds on transformers (^>=0.5.6.2); using transformers-0.6.1.0.
Reason: allow-newer enabled.
monadic-bang > build (lib)
monadic-bang > Preprocessing library for monadic-bang-0.1.0.0..
monadic-bang > Building library for monadic-bang-0.1.0.0..
monadic-bang > [6 of 8] Compiling MonadicBang.Utils [Source file changed]
monadic-bang > [7 of 8] Compiling MonadicBang.Internal
monadic-bang >
monadic-bang > <no location info>: error:
monadic-bang > panic! (the 'impossible' happened)
monadic-bang > GHC version 9.7.20230316:
monadic-bang > ltPSize
monadic-bang > HandleFailure
monadic-bang > Call stack:
monadic-bang > CallStack (from HasCallStack):
monadic-bang > callStackDoc, called at compiler/GHC/Utils/Panic.hs:189:37 in ghc:GHC.Utils.Panic
monadic-bang > pprPanic, called at compiler/GHC/Tc/Utils/TcType.hs:2428:5 in ghc:GHC.Tc.Utils.TcType
monadic-bang > CallStack (from HasCallStack):
monadic-bang > panic, called at compiler/GHC/Utils/Error.hs:454:29 in ghc:GHC.Utils.Error
monadic-bang >
monadic-bang >
monadic-bang > Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
monadic-bang >
```
## Expected behavior
Not panic.
## Environment
Optional:
* Operating System: macOS Ventura 13.2.1
* System Architecture: ARM M1
issue