[Concurrency] Remove * from backdeployed

This should have been a compile time error but seems it wasn't caught. Remove the * from the backDeployed as this is not something which makes sense and would break adopter projects.

Author: ktoso

stdlib/public/Concurrency/TaskGroup.swift

@@ -64,7 +64,7 @@ import Swift
 /// For tasks that need to handle cancellation by throwing an error,
 /// use the `withThrowingTaskGroup(of:returning:body:)` method instead.
 @available(SwiftStdlib 5.1, *)
-@backDeployed(before: SwiftStdlib 6.0, *)
+@backDeployed(before: SwiftStdlib 6.0)
 @inlinable
 public func withTaskGroup<ChildTaskResult, GroupResult>(
   of childTaskResultType: ChildTaskResult.Type,