action group button missing border

[snowystinger]

Closes

We use isolation in a couple places, the ActionGroup is very contained, so I don't think setting isolation on it should cause an issue. It allows us to make a very small change to support showing the correct border.

potentially a way to address #2653

Another option we could do is to bump the z-index of everything except the disabled case. This might interfere if someone is using z-index elsewhere in their app, though typically people reach for like, 10-100-999999, sooo that should be fairly safe too since we'd only go to about 5.
And yet another option could be to track which disabled buttons have non-disabled buttons before them and add the regular border to their leading edge. This has more room for error because it only applies to a couple of cases, we wouldn't want to do it when the buttons don't share an edge.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[adobe-bot]

Build successful! 🎉

• View the storybook
• View the storybook-16
• View the documentation

[devongovett]

Seems fine to me 🤷

[adobe-bot]

Build successful! 🎉

• View the storybook
• View the storybook-16
• View the documentation