Replace dead link in `CupertinoPicker` documentation (#135897)

This PR is a trivial change that replaces a dead link in `CupertinoPicker`'s [documentation](https://api.flutter.dev/flutter/cupertino/CupertinoPicker-class.html).

packages/flutter/lib/src/cupertino/picker.dart

@@ -49,7 +49,7 @@ const double _kOverAndUnderCenterOpacity = 0.447;
 ///
 ///  * [ListWheelScrollView], the generic widget backing this picker without
 ///    the iOS design specific chrome.
-///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/pickers/>
+///  * <https://developer.apple.com/design/human-interface-guidelines/pickers/>
 class CupertinoPicker extends StatefulWidget {
   /// Creates a picker from a concrete list of children.
   ///