Check that PolyFunction are not param-dependent

These are not supposed to be supported

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1184,6 +1184,7 @@ class Definitions {
       def isValidMethodType(info: Type) = info match
         case info: MethodType =>
           !info.resType.isInstanceOf[MethodOrPoly] // Has only one parameter list
+          && !info.isParamDependent
         case _ => false
       info match
         case info: PolyType => isValidMethodType(info.resType)