chore(python): add nox session to sort python imports (#326)

Source-Link: googleapis/synthtool@1b71c10
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:00c9d764fd1cd56265f12a5ef4b99a0c9e87cf261018099141e2ca5158890416

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

bigquery-datatransfer/snippets/conftest.py

@@ -20,12 +20,9 @@
 from google.api_core import client_options
 import google.api_core.exceptions
 import google.auth
-from google.cloud import bigquery
-from google.cloud import bigquery_datatransfer
-from google.cloud import pubsub_v1
+from google.cloud import bigquery, bigquery_datatransfer, pubsub_v1
 import pytest
 
-
 RESOURCE_PREFIX = "python_bigquery_datatransfer_samples_snippets"
 RESOURCE_DATE_FORMAT = "%Y%m%d%H%M%S"
 RESOURCE_DATE_LENGTH = 4 + 2 + 2 + 2 + 2 + 2