Relax generic variance in Array.flatten

libraries/stdlib/src/kotlin/collections/Arrays.kt

@@ -30,7 +30,7 @@ public inline fun <reified T> Array<out T>?.orEmpty(): Array<out T> = this ?: ar
 /**
  * Returns a single list of all elements from all arrays in the given array.
  */
-public fun <T> Array<Array<out T>>.flatten(): List<T> {
+public fun <T> Array<out Array<out T>>.flatten(): List<T> {
     val result = ArrayList<T>(sumBy { it.size })
     for (element in this) {
         result.addAll(element)