fixed STREAMLABS_POLLY_VOICE typo

see 1d3410646d..3068cead0c (r915594390)

TTS/streamlabs_polly.py

@@ -38,7 +38,7 @@ class StreamlabsPolly:
         else:
             if not settings.config["settings"]["tts"]["streamlabs_polly_voice"]:
                 raise ValueError(
-                    f"Please set the config variable STREAMLABS_VOICE to a valid voice. options are: {voices}"
+                    f"Please set the config variable STREAMLABS_POLLY_VOICE to a valid voice. options are: {voices}"
                 )
             voice = str(settings.config["settings"]["tts"]["streamlabs_polly_voice"]).capitalize()
         body = {"voice": voice, "text": text, "service": "polly"}