Add test

Author: odersky

tests/pos/i6909.scala

@@ -0,0 +1,14 @@
+import scala.compiletime.memo
+trait Foo[A]
+
+
+trait Qux {
+  private[this] var x: Int | Null = null
+  def f = {
+    if (x == null) x = 22
+    x.asInstanceOf[Int]
+  }
+  def g = memo(new Foo[Int] {})
+//
+  //given as Foo[Int] = new Foo[Int] {}
+}