IOS 13 Combine Framework - @Published not working ("Unknown attribute 'Published'")

From the Xcode 11 Beta Release Notes (emphasis added):

The Foundation integration for the Combine framework is unavailable. The following Foundation and Grand Central Dispatch integrations with Combine are unavailable: KeyValueObserving, NotificationCenter, RunLoop, OperationQueue, Timer, URLSession, DispatchQueue, JSONEncoder, JSONDecoder, PropertyListEncoder, PropertyListDecoder, and the @Published property wrapper. (51241500)

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Update: This has been fixed with Xcode 11 beta 2. From the Xcode 11 Beta 2 Release Notes:

Resolved Issues

The Foundation integration for the Combine framework is now available. The following Foundation and Grand Central Dispatch integrations with Combine are available: KeyValueObserving, NotificationCenter, RunLoop, OperationQueue, Timer, URLSession, DispatchQueue, JSONEncoder, JSONDecoder, PropertyListEncoder, PropertyListDecoder, and the @Published property wrapper. (51241500)