chore(python): add nox session to sort python imports (#257)

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>

Author: gcf-owl-bot[bot]

bigquery-reservation/snippets/reservation_test.py

@@ -17,10 +17,7 @@
 import pytest
 import test_utils.prefixer
 
-from . import reservation_create
-from . import reservation_delete
-from . import reservation_update
-
+from . import reservation_create, reservation_delete, reservation_update
 
 # Reservation IDs are limited to 64 characters.
 reservation_prefixer = test_utils.prefixer.Prefixer(