Add subclasses case to test

Author: natsukagami

tests/init/pos/early-promote-simple.scala

@@ -1,4 +1,14 @@
 class P() {
     val a = 1
     List(this)
+}
+
+class Outer {
+    class Inner {
+        val b = a
+    }
+    val a = 5
+    val b = new Inner()
+    List(new Inner())
+    List(b)
 }