Fix docs

Author: nicolasstucki

library/src/scala/tasty/reflect/IsInstanceOf.scala

@@ -9,7 +9,7 @@ package reflect
      type Idx
      given ClassTag[Nat]
      given ClassTag[Succ]
-     given ClassTag[Z]
+     given ClassTag[Idx]
      def n: Nat
    }
    object RI extens R {
@@ -28,10 +28,10 @@ package reflect
    }
    val r1: R = RI
    val r2: R = RI
-   r1.x match {
-     case x: r2.Nat => // Should not match or should have an unchecked waring
-     case x: r1.Idx => // Should not match or should have an unchecked waring
-     case x: r1.Succ => // Should match only if r1.x is an r1.Succ under the constraints set in r1
+   r1.n match {
+     case n: r2.Nat => // Should not match or should have an unchecked waring
+     case n: r1.Idx => // Should not match or should have an unchecked waring
+     case n: r1.Succ => // Should match only if r1.n is an r1.Succ under the constraints set in r1
    }
    ```
 */