High contrast submenu items are highlighted with border #431

Description

When I focus on popup menu item with submenu, it adds border to all submenu items too (selection highlight is not fully broken, because item's background color updates correctly)

Here's screenshot

Steps to reproduce

1. Choose the github dark high contrast or github light high contrast theme
2. Right click on code or click on File menu
3. Focus on the menu item with arrow >

Version

v6.3.5

Theme

GitHub Dark High Contrast