Add regression tests for already fixed issues

Fixes #9228
Fixes #8963

Author: odersky

tests/pos/i8963.scala

@@ -0,0 +1,21 @@
+type Numeric = Double | Int
+
+sealed trait VarValues[T, C <: VarValues[T,C]] {
+  this: C =>
+  val arr: Array[T]
+}
+final case class VarDoubles(arr: Array[Double]) extends VarValues[Double, VarDoubles]
+final case class VarInts(arr: Array[Int]) extends VarValues[Int, VarInts]
+final case class VarStrs(arr: Array[String]) extends VarValues[String, VarStrs]
+
+def check7(a: VarValues[_,_], b: VarValues[_,_]): Unit = {
+  (a,b) match {
+    case (x:(VarDoubles|VarInts), y:(VarDoubles|VarInts)) =>
+      val x0: Iterator[Numeric] = x.arr.iterator
+      val y0: Iterator[Numeric] = y.arr.iterator
+      val l0: Iterator[(Numeric, Numeric)] = x0.zip(y0)
+      val ll0: Iterator[(Numeric, Numeric)]#GroupedIterator[(Numeric, Numeric)] = x0.zip(y0).sliding(2,1)
+      ???
+    case _ => ???
+  }
+}

tests/pos/i9228.scala

@@ -0,0 +1,18 @@
+object ABug {
+
+  class Graph { class Node }
+
+  def ltol[O](tb: List[O]): List[O] = ???
+
+  def gtoll(using g: Graph): List[List[g.Node]] = ???
+
+  object graph extends Graph
+  import graph._
+  given graph.type = graph
+
+  val osq: List[List[Node]] = gtoll
+
+  val r: List[List[Any ]] = ltol(gtoll)
+  val q: List[List[Node]] = ltol(gtoll)
+
+}