**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.


tests/providers/google/cloud/hooks/test_dataflow.py
'workerZone': 'test-zone',
    'zone': 'us-central1-f',
    'machineType': 'n1-standard-1',
}
BASE_STRING = 'airflow.providers.google.common.hooks.base_google.{}'
DATAFLOW_STRING = 'airflow.providers.google.cloud.hooks.dataflow.{}'
TEST_PROJECT = 'test-project'
TEST_JOB_ID = 'test-job-id'
TEST_LOCATION = 'custom-location'
DEFAULT_PY_INTERPRETER = 'python3'
class TestFallbackToVariables(unittest.TestCase):
    def test_support_project_id_parameter(self):
        mock_instance = mock.MagicMock()
        class FixtureFallback:
            @_fallback_to_project_id_from_variables
            def test_fn(self, *args, **kwargs):
                mock_instance(*args, **kwargs)
        FixtureFallback().test_fn(project_id="TEST")
        mock_instance.assert_called_once_with(project_id="TEST")
    def test_support_project_id_from_variable_parameter(self):
        mock_instance = mock.MagicMock()
        class FixtureFallback:
            @_fallback_to_project_id_from_variables
            def test_fn(self, *args, **kwargs):
                mock_instance(*args, **kwargs)
        FixtureFallback().test_fn(variables={'project': "TEST"})
        mock_instance.assert_called_once_with(project_id='TEST', variables={})
    def test_raise_exception_on_conflict(self):
        mock_instance = mock.MagicMock()
        class FixtureFallback: