Fix mouse cursor not changing on OS X during DND

The cursor almost always looks like the one used for copying. Add
missing breaks in a switch statement to fix this.

See #14726.

src/osx/cocoa/window.mm

@@ -1215,10 +1215,16 @@ unsigned int wxOnDraggingEnteredOrUpdated(wxWidgetCocoaImpl* viewImpl,
     {
         case wxDragLink:
             nsresult = NSDragOperationLink;
+            break;
+
         case wxDragMove:
             nsresult = NSDragOperationMove;
+            break;
+
         case wxDragCopy:
             nsresult = NSDragOperationCopy;
+            break;
+
         default :
             break;
     }