fix #5692 - Selecting an unavailable date should not change the current selection

[richardbann]

Closes #5692

✅ Pull Request Checklist:

• [ x] Included link to corresponding React Spectrum GitHub Issue.
• [ x] 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:

unit test and updated story

🧢 Your Project: