fix(Menu): show checkboxes for selected items with ContextualHelpTrigger isUnavailable={false}

[reidbarber]

Closes #8871

✅ 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:

Test new story: https://reactspectrum.blob.core.windows.net/reactspectrum/a205e07eb8f1f9b0b1d77d98fe70c2da574b41d3/storybook/index.html?path=/story/menutrigger--menu-item-unavailable-with-selection&providerSwitcher-express=false

🧢 Your Project:

[rspbot]

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