Add a regression test (#17102)

Author: dwijnand

tests/pos/i10369.scala

@@ -0,0 +1,15 @@
+type Upgrade[T] = T match
+  case Int => Double
+  case Char => String
+  case Boolean => Boolean
+
+val upgrade: [t] => t => Upgrade[t] = new PolyFunction:
+  def apply[T](x: T): Upgrade[T] = x match
+    case x: Int => x.toDouble
+    case x: Char => x.toString
+    case x: Boolean => !x
+
+val upgrade2: [t] => t => Upgrade[t] = [t] => (x: t) => x match
+  case x: Int => x.toDouble
+  case x: Char => x.toString
+  case x: Boolean => !x