Add selectionMode to Toolbar story

[yihuiliao]

Found during testing

Updates the story for Toolbar using actionGroup to use selectionMode so that it's easy to show it working with touch

✅ 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:

Link to Toolbar story

When you select on the items, they should visually appear to be selected.

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-17
• View the storybook-16
• View the documentation

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-17
• View the storybook-16
• View the documentation

[rspbot]

## API Changes

unknown top level export { type: 'identifier', name: 'Column' }
unknown top level export { type: 'identifier', name: 'Column' }
unknown type { type: 'link' }
unknown type { type: 'link' }
unknown type { type: 'link' }
unknown type { type: 'link' }
unknown type { type: 'link' }
unknown type { type: 'link' }