**What happened**:

With the new Backport providers, when calling `DataflowCreatePythonJobOperator` with an empty `py_rerquirments` Dataflow commands always launch inside a virtualenv.

**What you expected to happen**:

The Dataflow command should run locally.


airflow/providers/google/cloud/operators/dataflow.py
self, *,
            py_file: str,
            job_name: str = '{{task.task_id}}',
            dataflow_default_options: Optional[dict] = None,
            options: Optional[dict] = None,
            py_interpreter: str = "python3",
            py_options: Optional[List[str]] = None,
            py_requirements: Optional[List[str]] = None,
            py_system_site_packages: bool = False,
            project_id: Optional[str] = None,
            location: str = DEFAULT_DATAFLOW_LOCATION,
            gcp_conn_id: str = 'google_cloud_default',
            delegate_to: Optional[str] = None,
            poll_sleep: int = 10,
            **kwargs) -> None:
        super().__init__(**kwargs)
        self.py_file = py_file
        self.job_name = job_name
        self.py_options = py_options or []
        self.dataflow_default_options = dataflow_default_options or {}
        self.options = options or {}
        self.options.setdefault('labels', {}).update(
            {'airflow-version': 'v' + version.replace('.', '-').replace('+', '-')})
        self.py_interpreter = py_interpreter