not constrain if formal contains instantiated type vars

Author: Alex1005a

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -4364,7 +4364,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             val tm = new TypeMap:
               def apply(t: Type): Type = t match
                 case tvar: TypeVar =>
-                  formalConstrained |= ctx.typerState.constraint.contains(tvar)
+                  formalConstrained |= ctx.typerState.constraint.contains(tvar) || tvar.instanceOpt.exists
                   val inst = tvar.instanceOpt
                   if (inst.exists && !formalConstrained) mapOver(inst) else tvar
                 case _ =>