The GCSToLocalFilesystemOperator in Google Provider <=3.0.0  had wrong import for apply_defaults. It used

```
from airflow.sensors.base_sensor_operator import apply_defaults
```

instead of 

```
from airflow.utils.decorators import apply_defaults
```

When we removed `apply_defaults` in #15667, the base_sensor_operator import was removed as well which made the GCSToLocalFilestystemOperator stops working in 2.1.0

The import in base_sensor_operator will be restored in 2.1.1  and Google Provider 4.0.0 will work without problems after it is released. Workaround for 2.1.0 Airflow is to copy the code of the operator to DAG and use it temporarily until new versions are released. 
airflow/sensors/base.py
"""
        Function that the sensors defined while deriving this class should
        override.
        """
        raise AirflowException('Override me.')
    def is_smart_sensor_compatible(self):
        check_list = [
            not self.sensor_service_enabled,
            self.on_success_callback,
            self.on_retry_callback,
            self.on_failure_callback,
        ]
        for status in check_list:
            if status:
                return False
        operator = self.__class__.__name__
        return operator in self.sensors_support_sensor_service
    def register_in_sensor_service(self, ti, context):