Speech API python client library method `streaming_recognize()` doesn't return a result with `is_final` set to True

## In which file did you encounter the issue?
- https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/speech/microphone/transcribe_streaming_infinite.py

## Did you change the file? If so, how?
I have changed the line 299
```
config = speech.RecognitionConfig(
encoding=speech.RecognitionConfig.AudioEncoding.LINEAR16,
sample_rate_hertz=SAMPLE_RATE,
language_code="en-US",
max_alternatives=1,
)
```
into
```
config = speech.RecognitionConfig(
encoding=speech.RecognitionConfig.AudioEncoding.LINEAR16,
sample_rate_hertz=SAMPLE_RATE,
language_code="ja-JP",
max_alternatives=1,
)
```

## Describe the issue
streaming_recognize() method doesn't work properly. For even when a speaker utters a simple greeting like こんにちは in a very silent environment, this method returns StreamingRecognizeResponse object with a result of is_final == False. And always returns a result with is_final set to True exactly 90 seconds later.
this doesn't happen when the language is English or Chinese.
The same thing also happens in `transcribe_streaming_infinite_v2.py`

I am not sure if this report should be post here for this seems to be more internal problem.
Appreciate any help or clues anyways.