Minor, add test case on SAM conversion over smart cast

compiler/testData/codegen/box/sam/castFromAny.kt

@@ -0,0 +1,14 @@
+// TARGET_BACKEND: JVM
+
+fun test(a: Any?) {
+    a as () -> Unit
+    Runnable(a).run()
+}
+
+fun box(): String {
+    var result = "Fail"
+    test {
+        result = "OK"
+    }
+    return result
+}