panic when typing x=5:x into GHCi

Summary

In GHCi, version 9.3.20210619:

ghci> x=5:x
ghc: panic! (the 'impossible' happened)
  GHC version 9.3.20210619:
        nameModule
  internal x1_sCB
  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/Types/Name.hs:323:3 in ghc:GHC.Types.Name

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

Expected Behavior

Don't panic