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**Apache Airflow version**: 2.0.0


**Kubernetes version (if you are using kubernetes)** (use `kubectl version`): 1.16.15-gke.4901

**Environment**:

- **Cloud provider or hardware configuration**: GKE
- **OS** (e.g. from /etc/os-release): 
- **Kernel** (e.g. `uname -a`): 
- **Install tools**: Using the apache/airflow docker image
- **Others**: Running 1 pod encapsulating 2 containers (1 x webserver and 1x scheduler) running in localexecutor mode

**What happened**:

I have remote logging configured for tasks to send the logs to StackDriver as per the below configuration.  The logs get sent to Stackdriver okay and I can view them via the GCP console.  However I cannot view them when browsing the UI.

The UI shows a spinning wheel and I see requests in the network tab to 
`https://my_airflow_instance/get_logs_with_metadata?dag_id=XXX......`

These requests take about 15 seconds to run before returning with HTTP 200 and something like this in the response body:

```
{"message":"","metadata":{"end_of_log":false,"next_page_token":"xxxxxxxxx"}}
```

So no actual log data

**What you expected to happen**:

I should see the logs in the Web UI

**How to reproduce it**:

Configure remote logging for StackDriver with the below config:

```
  AIRFLOW__LOGGING__GOOGLE_KEY_PATH: "/var/run/secrets/airflow/secrets/google-cloud-platform/stackdriver/credentials.json"
  AIRFLOW__LOGGING__LOG_FORMAT: "[%(asctime)s] {{%(filename)s:%(lineno)d}} %(levelname)s - %(message)s"
  AIRFLOW__LOGGING__REMOTE_LOGGING: "True"
  AIRFLOW__LOGGING__REMOTE_BASE_LOG_FOLDER: "stackdriver://airflow-tasks"
```

**Anything else we need to know**:

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airflow/providers/google/cloud/log/stackdriver_task_handler.py
self, task_instance: TaskInstance, try_number: Optional[int] = None, metadata: Optional[Dict] = None
    ) -> Tuple[List[str], List[Dict]]:
        """
        Read logs of given task instance from Stackdriver logging.
        :param task_instance: task instance object
        :type task_instance: :class:`airflow.models.TaskInstance`
        :param try_number: task instance try_number to read logs from. If None
           it returns all logs
        :type try_number: Optional[int]
        :param metadata: log metadata. It is used for steaming log reading and auto-tailing.
        :type metadata: Dict
        :return: a tuple of list of logs and list of metadata
        :rtype: Tuple[List[str], List[Dict]]
        """
        if try_number is not None and try_number < 1:
            logs = [f"Error fetching the logs. Try number {try_number} is invalid."]
            return logs, [{"end_of_log": "true"}]
        if not metadata:
            metadata = {}
        ti_labels = self._task_instance_to_labels(task_instance)
        if try_number is not None:
            ti_labels[self.LABEL_TRY_NUMBER] = str(try_number)
        else:
            del ti_labels[self.LABEL_TRY_NUMBER]
        log_filter = self._prepare_log_filter(ti_labels)
        next_page_token = metadata.get("next_page_token", None)
        all_pages = 'download_logs' in metadata and metadata['download_logs']