Replaced to async method for URLSessionWebSocketTask.receive().

[kitwtnb]

Using MainActor properties in an unstructured task would cause build errors in Swift 6, so URLSessionWebSocketTask.receive(completionHandler:) was replaced with URLSessionWebSocketTask.receive() async throws.

[Dimillian]

This is cool thanks! Will try in a bit and merge!

[Dimillian]

This is weird, I've been testing it extensively and never received any message.