Fix #12544: Add test

Author: liufengyun

tests/init/pos/i12544.scala

@@ -0,0 +1,12 @@
+enum Enum:
+  case Case
+
+object Enum:
+  object nested:
+    val a: Enum = Case
+
+  val b: Enum = f(nested.a)
+
+  def f(e: Enum): Enum = e
+
+@main def main(): Unit = println(Enum.b)