Chirp3 HD Voices don't support markup field in long audio synthesis

[gaieges]

I'm trying to put some pauses in my synthesized text-to-speech audio.  Since it seems as though the Chirp3 HD voices don't support SSML 🙁 , I attempted to use the `markup` functionality described here:

https://cloud.google.com/text-to-speech/docs/chirp3-hd#pause_control

When trying this with the latest (2.25.1) python library, it fails with the following error message:

Unknown field for SynthesisInput: markup

Code:

operation = client.synthesize_long_audio(
  timeout=600,
  request=texttospeech.SynthesizeLongAudioRequest(
    parent=client.common_location_path(
      CONFIG.firebase_project, CONFIG.firebase_location
    ),
    input={"markup": text},
    voice=voice,
    audio_config=audio_config,
    output_gcs_uri=output_url,
  ),
)
return operation.result(timeout=600)