Add original issue test

Fixes #23435

Author: EugeneFlesselle

tests/neg/i23435-min.scala

@@ -0,0 +1,6 @@
+
+type Or[+A, +B] = A | B
+
+val x: Or[Int, String] & Or[String, Int] = 3
+val y: Or[Int & String, Int & String] = x // error
+val z: Int & String = y

tests/neg/i23435.scala

@@ -0,0 +1,16 @@
+
+trait L[+A]{val a:A}
+trait R[+B]{val b: B}
+
+class LR(val a: Int, val b: String) extends L[Int] with R[String]
+
+type E[+A] = L[A] | R[A]
+
+val x: E[Int] & E[String] = LR(4, "hi")
+val y: E[Int&String] = x // error
+
+val z = y match
+  case l : L[Int&String] => l.a
+  case r : R[Int&String] => r.b
+
+val _ = z:String // was: java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.String