[menu] SRs initially not announcing first menuItem in a menu

• [ X ] The issue is present in the latest release.
• [ X ] I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

When the user opens a menu, the screen reader does not announce the focussed/first item within the menu.

Expected Behavior 🤔

Once a user opens a menu, the first menuItem that is focussed should be announced by the screen reader.

Steps to Reproduce 🕹

https://codesandbox.io/s/mui-icon-button-menu-gomtg

Steps:

With the relevant screen readers enabled:

1. Tab to the Icon Button
2. Press Space or Enter to Open the menu
3. Once opened, notice that the first item in the list does not get announced by the relevant screen readers

Context 🔦

It would be great if the relevant screen readers could announce the text of the first menu item once the menu is opened.

Your Environment 🌎