IArray.toArray: Fix unsound cast

This changes the result type in a binary-compatible way since `Array[T]`
and `Array[? <: T]` both erase to `Object` here.

Author: smarter

library/src/scala/IArray.scala

@@ -250,8 +250,8 @@ object IArray:
     genericArrayOps(arr).takeWhile(p)
 
   /** Returns a mutable copy of this immutable array. */
-  extension [T](arr: IArray[T]) def toArray: Array[T] =
-    arr.clone.asInstanceOf[Array[T]]
+  extension [T](arr: IArray[T]) def toArray: Array[? <: T] =
+    arr.clone
 
   extension [T](arr: IArray[T])
     def ++[U >: T: ClassTag](suffix: IArray[U]): IArray[U] = genericArrayOps(arr) ++ suffix.toSeq

tests/neg/i12597.scala

@@ -0,0 +1,5 @@
+@main def Test =
+  val a: IArray[Int] = IArray(2)
+  val b: IArray[Any] = a
+  val c = b.toArray
+  c(0) = "" // error: Found: String Required: c.T

tests/run/i12597.scala

@@ -0,0 +1,4 @@
+@main def Test =
+  val a: IArray[Int] = IArray(2)
+  val b: IArray[Any] = a
+  b.toArray