**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
#
#
#
"""
This module contains a Google Dataflow Hook.
"""
import functools
import json
import re
import select
import shlex
import subprocess
import time
import uuid
import warnings
from copy import deepcopy
from tempfile import TemporaryDirectory
from typing import Any, Callable, Dict, List, Optional, Sequence, TypeVar, Union, cast
from googleapiclient.discovery import build
from airflow.exceptions import AirflowException
from airflow.providers.google.common.hooks.base_google import GoogleBaseHook
from airflow.utils.log.logging_mixin import LoggingMixin
from airflow.utils.python_virtualenv import prepare_virtualenv
DEFAULT_DATAFLOW_LOCATION = 'us-central1'
JOB_ID_PATTERN = re.compile(
    r'Submitted job: (?P<job_id_java>.*)|Created job with id: \[(?P<job_id_python>.*)\]'
)
T = TypeVar("T", bound=Callable)  
def _fallback_variable_parameter(parameter_name: str, variable_key_name: str) -> Callable[[T], T]: