fix: mark menuAlignment as optional in MenuButton (#18659)

Co-authored-by: Riddhi Bansal <41935566+riddhybansal@users.noreply.github.com>

Author: adamalston

packages/react/src/components/MenuButton/index.tsx

@@ -70,7 +70,7 @@ export interface MenuButtonProps extends ComponentProps<'div'> {
   /**
    * Experimental property. Specify how the menu should align with the button element
    */
-  menuAlignment: MenuAlignment;
+  menuAlignment?: MenuAlignment;
 
   /**
    * Specify the size of the button and menu.
@@ -248,7 +248,6 @@ MenuButton.propTypes = {
   /**
    * Experimental property. Specify how the menu should align with the button element
    */
-  // @ts-ignore-next-line -- avoid spurious (?) TS2322 error
   menuAlignment: PropTypes.oneOf([
     'top',
     'top-start',