Widen skolem types when adding parent refinements (#22488)

closes #22456

Author: KacperFKorban

Diff for: compiler/src/dotty/tools/dotc/core/NamerOps.scala

@@ -39,14 +39,17 @@ object NamerOps:
    */
   extension (tp: Type)
     def separateRefinements(cls: ClassSymbol, refinements: mutable.LinkedHashMap[Name, Type] | Null)(using Context): Type =
+      val widenSkolemsMap = new TypeMap:
+        def apply(tp: Type) = mapOver(tp.widenSkolem)
       tp match
         case RefinedType(tp1, rname, rinfo) =>
           try tp1.separateRefinements(cls, refinements)
           finally
             if refinements != null then
+              val rinfo1 = widenSkolemsMap(rinfo)
               refinements(rname) = refinements.get(rname) match
-                case Some(tp) => tp & rinfo
-                case None => rinfo
+                case Some(tp) => tp & rinfo1
+                case None => rinfo1
         case tp @ AnnotatedType(tp1, ann) =>
           tp.derivedAnnotatedType(tp1.separateRefinements(cls, refinements), ann)
         case tp: RecType =>

Diff for: tests/pos/i22456.scala

@@ -0,0 +1,4 @@
+import language.experimental.modularity
+
+class T(tracked val y: Int)
+class C(tracked val x: Int) extends T(x + 1)