**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/hooks/dataflow.py
job_id=job_id,
            location=location,
            poll_sleep=self.poll_sleep,
            num_retries=self.num_retries)
        jobs_controller.wait_for_done()
        return response["job"]
    @_fallback_to_location_from_variables
    @_fallback_to_project_id_from_variables
    @GoogleBaseHook.fallback_to_default_project_id
    def start_python_dataflow(  
        self,
        job_name: str,
        variables: Dict,
        dataflow: str,
        py_options: List[str],
        project_id: str,
        py_interpreter: str = "python3",
        py_requirements: Optional[List[str]] = None,
        py_system_site_packages: bool = False,
        append_job_name: bool = True,
        on_new_job_id_callback: Optional[Callable[[str], None]] = None,
        location: str = DEFAULT_DATAFLOW_LOCATION
    ):
        """
        Starts Dataflow job.
        :param job_name: The name of the job.
        :type job_name: str
        :param variables: Variables passed to the job.
        :type variables: Dict
        :param dataflow: Name of the Dataflow process.