fix: table dnd keyboard navigation

[chirokas]

Closes

• Fix a crash during DnD keyboard navigation in RAC Table.
• Skip non-item nodes (e.g., tablebody, loader) since they can't be drop targets.

✅ 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:

In the Dnd Table Example/tableview dnd story, start a keyboard drag session and hold ArrowUp to cycle through the table multiple times.

🧢 Your Project: