Building HEAD devel2 flavour panics in CorePrep

Steps to reproduce

Check out a clean master at 13d3c613. Boot, configure, and run hadrian/build -o_corePrepBug --flavour=devel2. This eventually fails while compiling _corePrepBug/stage1/compiler/build/GHC/Parser/Lexer.hs with the following panic:

ghc: panic! (the 'impossible' happened)
  GHC version 9.9.20231014:
        cpeBind
  Case top-lvl sat_sj8D :: Ord [Char]
               [LclId]
               sat_sj8D = $fOrdList @Char $fOrdChar
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/GHC/Utils/Panic.hs:186:37 in ghc:GHC.Utils.Panic
        pprPanic, called at compiler/GHC/CoreToStg/Prep.hs:652:46 in ghc:GHC.CoreToStg.Prep
  CallStack (from HasCallStack):
    panic, called at compiler/GHC/Utils/Error.hs:511:29 in ghc:GHC.Utils.Error


Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

Expected behavior

...successful build...

Environment

• GHC version used: master at 13d3c613
• Alex version 3.4.0.0

---

This probably indicates a bug in the very recently merged !11368 (closed). (cc @sgraf812)