[K/N][Tests] Adjust moved codegen tests to new infra

^KT-61259

native/native.tests/testData/codegen/branching/when8.kt

@@ -3,13 +3,11 @@
  * that can be found in the LICENSE file.
  */
 
-package codegen.branching.when8
-
 import kotlin.test.*
 
-@Test fun runTest() {
+fun box(): String {
     when (true) {
-        true -> println("true")
-        false -> println("false")
+        true -> return "OK"
+        false -> return "FAIL"
     }
 }