Update iframeHeight in EmptyState story for Menu component

- Increased the `iframeHeight` from 300 to 500 in the `EmptyState` story, improving the rendering context for better visibility and usability in the documentation.
- This change enhances the overall presentation of the Menu component's story, ensuring it displays correctly in the documentation environment.

Author: codingwolf-at

packages/propel/src/components/menu/menu.stories.tsx

@@ -840,7 +840,7 @@ export const EmptyState: Story = {
     docs: {
       story: {
         inline: false,
-        iframeHeight: 300,
+        iframeHeight: 500,
       },
     },
   },