fix(HierarchicalMenu): don't give --parent class if data is empty

[Haroenv]

Summary

This happens when the item is refined, but there's no items in the lower level. In InstantSearch.js and React InstantSearch Dom, we avoid adding the class in this case already:

instantsearch/packages/instantsearch.js/src/components/RefinementList/RefinementList.tsx

Lines 175 to 179 in f84c01b

	Boolean(
	isHierarchicalMenuItem(facetValue) &&
	Array.isArray(facetValue.data) &&
	facetValue.data.length > 0
	) && this.props.cssClasses.parentItem!

instantsearch/packages/react-instantsearch-dom/src/components/List.js

Lines 64 to 75 in f84c01b

	const itemHasChildren = item.items && Boolean(item.items.length);
	return (
	<li
	key={item.key || item.label}
	className={this.props.cx(
	'item',
	item.isRefined && 'item--selected',
	item.noRefinement && 'item--noRefinement',
	itemHasChildren && 'item--parent'
	)}
	>

detected in #5456

Result

ais-HierarchicalMenu-item--parent is not applied when children are empty, even if it is refined. This makes React InstantSearch Hooks and Vue InstantSearch consistent with the other flavours.

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[dhayab]

Could we amend our tests to cover this case?