fix: don't drop state during update in Param.toMono (#8582)

This PR fixes an accidental dropping of state in Param.toMono. When this
code was originally written, there was no other state besides
`typeParams`.

Author: zwarich

src/Lean/Compiler/LCNF/ToMono.lean

@@ -19,7 +19,7 @@ abbrev ToMonoM := StateRefT ToMonoM.State CompilerM
 
 def Param.toMono (param : Param) : ToMonoM Param := do
   if isTypeFormerType param.type then
-    modify fun { typeParams, .. } => { typeParams := typeParams.insert param.fvarId }
+    modify fun s => { s with typeParams := s.typeParams.insert param.fvarId }
   param.update (← toMonoType param.type)
 
 def isTrivialConstructorApp? (declName : Name) (args : Array Arg) : ToMonoM (Option LetValue) := do