Remove shadow above expanded Menu Items

[Rldeckard]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

There is a shadow that should not exist above/on top of expanded Menus. This makes the Menu Items look disconnected from the dropdown like a pop up window. Removing the top shadow will make the menu appear attached to the calling button as is expected functionality.

How to reproduce

1. Create Fyne Menu.
2. Add NewMenuItem.
3. Run code and click on Menu.
4. Observe Shadow above submenu / list.
5. Open notepad and click file to observe shadows on the right and bottom, but not above the list.

Screenshots

Example code

menu := fyne.NewMenu("Help", fyne.NewMenuItem("About", func() {}))

Fyne version

2.3.5

Go compiler version

1.20.2

Operating system and version

Windows 10

Additional Information

No response