Fix tvOS build error with Swift 6.3 for SFSpeech extensions

[davdroman]

The SFSpeechRecognizerAuthorizationStatus, SFSpeechRecognitionTaskHint, and SFSpeechRecognitionTaskState types are unavailable on tvOS, but the @available attributes on their CustomDumpStringConvertible conformances didn't reflect this. Starting with Swift 6.3, this causes a build error:

error: 'SFSpeechRecognizerAuthorizationStatus' is unavailable in tvOS
extension SFSpeechRecognizerAuthorizationStatus: CustomDumpStringConvertible {
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error: 'SFSpeechRecognitionTaskHint' is unavailable in tvOS
extension SFSpeechRecognitionTaskHint: CustomDumpStringConvertible {
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~

error: 'SFSpeechRecognitionTaskState' is unavailable in tvOS
extension SFSpeechRecognitionTaskState: CustomDumpStringConvertible {
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

This adds @available(tvOS, unavailable) to each of the three extensions.