fix(table): make TableHeaderProps.columns accept readonly arrays

[sonsu-lee]

Closes #5625

✅ 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:

• Type change only. No runtime impact.

🧢 Your Project:

• Personal contribution