Remove Task.CancellationError in doc comments (#41107)

Task.CancellationError has been renamed to CancellationError. Fix two doc comments that still used the old name.

Co-authored-by: Ole Begemann <[email protected]>

Author: ktoso

stdlib/public/Concurrency/Task.swift

@@ -100,7 +100,7 @@ extension Task {
   /// depending on the executor's scheduling details.
   ///
   /// If the task throws an error, this property propagates that error.
-  /// Tasks that respond to cancellation by throwing `Task.CancellationError`
+  /// Tasks that respond to cancellation by throwing `CancellationError`
   /// have that error propagated here upon cancellation.
   ///
   /// - Returns: The task's result.

stdlib/public/Concurrency/TaskCancellation.swift

@@ -72,7 +72,7 @@ extension Task where Success == Never, Failure == Never {
 extension Task where Success == Never, Failure == Never {
   /// Throws an error if the task was canceled.
   ///
-  /// The error is always an instance of `Task.CancellationError`.
+  /// The error is always an instance of `CancellationError`.
   ///
   /// - SeeAlso: `isCancelled()`
   public static func checkCancellation() throws {