ComboBox: aXe throws an error when the virtualized listbox is scrollable

# 🐛 Bug Report 

While testing MobileComboBox variant that opens within a Tray using [ComboBox example with many items](https://react-spectrum.adobe.com/react-spectrum/ComboBox.html#sections) example, aXe throws an error when the virtualized listbox is scrollable, [Scrollable region must have keyboard access](https://dequeuniversity.com/rules/axe/4.6/scrollable-region-focusable?application=AxeChrome), because the listbox and any of its descendant option items do not have a `tabIndex`.

This relates to the following commit, which removes `tabIndex` from the listbox and descendant option items for virtualized listboxes that use `aria-activedescendant`: [Remove tabIndex from listbox and options when using virtual focus: iOS 14 moves real DOM focus even with aria-activedescendant otherwise](https://github.com/adobe/react-spectrum/pull/1176/commits/3d82fda7ab4280bc775c9d32cce39b02f7c3a1ec).

See the code comments for this behavior as well: 
https://github.com/adobe/react-spectrum/blob/0f953cac84f98cdff29f2348c120ce541ebb6da8/packages/%40react-aria/selection/src/useSelectableItem.ts#L151-L164

and:
https://github.com/adobe/react-spectrum/blob/0f953cac84f98cdff29f2348c120ce541ebb6da8/packages/%40react-aria/selection/src/useSelectableCollection.ts#L390-L397

## 🤔 Expected Behavior

aXe should not throw this false positive on platforms where it is not necessary to remove the `tabIndex`.

## 😯 Current Behavior

aXe throws an error when the virtualized listbox is scrollable, [Scrollable region must have keyboard access](https://dequeuniversity.com/rules/axe/4.6/scrollable-region-focusable?application=AxeChrome), because the listbox and any of its descendant option items do not have a `tabIndex`.

## 💁 Possible Solution

We might be able to safely remove the `tabIndex` attributes for a virtualized listbox only on mobile devices.

## 🔦 Context

Accessibility audit

## 🌍 Your Environment



| Software         | Version(s) |
| ---------------- | ---------- |
| react-spectrum   |  [@adobe/react-spectrum@3.24.1](https://github.com/adobe/react-spectrum/releases/tag/%40adobe%2Freact-spectrum%403.24.1)
| Browser          |  Google Chrome Version 110.0.5481.77 (Official Build) (arm64)
| Operating System | macOS Ventura 13.2.1 (22D68)

## 🧢 Your Company/Team

Adobe/Accessibility

## 🕷 Tracking Issue (optional)

A11Y-5821

	// Set tabIndex to 0 if the element is focused, or -1 otherwise so that only the last focused
	// item is tabbable. If using virtual focus, don't set a tabIndex at all so that VoiceOver
	// on iOS 14 doesn't try to move real DOM focus to the item anyway.
	let itemProps: SelectableItemAria['itemProps'] = {};
	if (!shouldUseVirtualFocus && !isDisabled) {
	itemProps = {
	tabIndex: key === manager.focusedKey ? 0 : -1,
	onFocus(e) {
	if (e.target === ref.current) {
	manager.setFocusedKey(key);
	}
	}
	};
	} else if (isDisabled) {

	// If nothing is focused within the collection, make the collection itself tabbable.
	// This will be marshalled to either the first or last item depending on where focus came from.
	// If using virtual focus, don't set a tabIndex at all so that VoiceOver on iOS 14 doesn't try
	// to move real DOM focus to the element anyway.
	let tabIndex: number;
	if (!shouldUseVirtualFocus) {
	tabIndex = manager.focusedKey == null ? 0 : -1;
	}

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ComboBox: aXe throws an error when the virtualized listbox is scrollable #4080

🐛 Bug Report

🤔 Expected Behavior

😯 Current Behavior

💁 Possible Solution

🔦 Context

🌍 Your Environment

🧢 Your Company/Team

🕷 Tracking Issue (optional)

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Software	Version(s)
react-spectrum	@adobe/[email protected]
Browser	Google Chrome Version 110.0.5481.77 (Official Build) (arm64)
Operating System	macOS Ventura 13.2.1 (22D68)