add a new tts piper model (k2-fsa#927)

Author: csukuangfj

scripts/apk/generate-tts-apk-script.py

@@ -125,6 +125,7 @@ def get_piper_models() -> List[TtsModel]:
         TtsModel(model_dir="vits-piper-en_GB-northern_english_male-medium"),
         TtsModel(model_dir="vits-piper-en_GB-semaine-medium"),
         TtsModel(model_dir="vits-piper-en_GB-southern_english_female-low"),
+        TtsModel(model_dir="vits-piper-en_GB-southern_english_female-medium"),
         TtsModel(model_dir="vits-piper-en_GB-sweetbbak-amy"),
         TtsModel(model_dir="vits-piper-en_GB-vctk-medium"),
         TtsModel(model_dir="vits-piper-en_US-amy-low"),