Replace deprecated join with joinToString in testData

compiler/testData/codegen/boxWithStdlib/reified/copyToArray.kt

@@ -6,10 +6,10 @@ inline fun <reified T> copy(c: Collection<T>): Array<T> {
 
 fun box(): String {
     val a: Array<String> = copy(listOf("a", "b", "c"))
-    assertEquals("abc", a.join(""))
+    assertEquals("abc", a.joinToString(""))
 
     val b: Array<Int> = copy(listOf(1,2,3))
-    assertEquals("123", b.map { it.toString() }.join(""))
+    assertEquals("123", b.map { it.toString() }.joinToString(""))
 
     return "OK"
 }