Icon button groups wiggle around while on hover

### Description

Hover the different icon buttons of a group and the borders will shift
https://user-images.githubusercontent.com/12767551/220979714-66b8ba95-2f3d-4198-8503-132f6bb48a4c.mov



### Steps to reproduce

1. Got to https://primer.style/react/ButtonGroup
2. Hover over the buttons in the icon button group

### Version

v35.20.0

### Browser

Chrome