fix: gridlist section accessibility updates

[yihuiliao]

just fixes the invalid aria the MJ pointed out #8790 (comment)

the other stuff regarding the aria-rowcount can be fixed separately since it is in alpha

✅ 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:

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## API Changes

react-aria-components

/react-aria-components:GridListHeaderContext

+GridListHeaderContext {
+  UNTYPED
+}

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