Fix typo in BoundedBufferStateMachine

Author: GavrilikArt

Sources/AsyncAlgorithms/Buffer/BoundedBufferStateMachine.swift

@@ -64,7 +64,7 @@ struct BoundedBufferStateMachine<Base: AsyncSequence> {
   mutating func shouldSuspendProducer() -> Bool {
     switch state {
       case .initial:
-        preconditionFailure("Invalid state. The task should already by started.")
+        preconditionFailure("Invalid state. The task should already be started.")
 
       case .buffering(_, let buffer, .none, .none):
         // we are either idle or the buffer is already in use (no awaiting consumer)