ToggleGroup - fix issue where button rounding doesn't align with toggle group border-radius

[jcfilben]

What does this PR do?

There is a slight gap in the rounding between the border of the ToggleGroup container and the buttons within. It is easiest to see this in the dark mode grommet theme. This PR fixes this so that there isn't a gap.
before:

after:

Where should the reviewer start?

What testing has been done on this PR?

How should this be manually tested?

Do Jest tests follow these best practices?

• screen is used for querying.
• The correct query is used. (Refer to this list of queries)
• asFragment() is used for snapshot testing.

Any background context you want to provide?

What are the relevant issues?

Screenshots (if appropriate)

Do the grommet docs need to be updated?

no

Should this PR be mentioned in the release notes?

yes

Is this change backwards compatible or is it a breaking change?

backwards compatible

[taysea]

This solution seems to crop out the focus indicator.

Screen.Recording.2024-05-21.at.1.19.43.PM.mov

[jcfilben]

This solution seems to crop out the focus indicator.

Oops, good catch. Marking this PR as a draft. I'll have to think about other approaches we can take to solve this